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1.
Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.  相似文献   

2.
Sediment balances in the Blue Nile River Basin   总被引：2，自引：1，他引：1  
Rapid population growth in the upper Blue Nile basin has led to fast land-use changes from natural forest to agricultural land.This resulted in speeding up the soil erosion process in the highlands and increasing sedimentation further downstream in reservoirs and irrigation canals.At present,several dams are planned across the Blue Nile River in Ethiopia and the Grand Ethiopian Renaissance Dam is currently under construction near the border with Sudan.This will be the largest hydroelectric power plant in Africa.The objective of this paper is to quantify the river flows and sediment loads along the Blue Nile River network.The Soil and Water Assessment Tool was used to estimate the water flows from un-gauged sub-basins.To assess model performance,the estimated sediment loads were compared to the measured ones at selected locations.For the gauged sub-basins,water flows and sediment loads were derived from the available flow and sediment data.To fill in knowledge gaps,this study included a field survey in which new data on suspended solids and flow discharge were collected along the Blue Nile and on a number of tributaries.The comparison between the results of this study and previous estimates of the sediment load of the Blue Nile River at El Deim,near the Ethiopian Sudanese border,show that the sediment budgets have the right order of magnitude,although some uncertainties remain.This gives confidence in the results of this study providing the first sediment balance of the entire Blue Nile catchment at the sub-basin scale.  相似文献   

3.
In this study, monthly and annual Upper Blue Nile Basin rainfall data were analyzed to learn the rainfall statistics and its temporal and spatial distribution. Frequency analysis and spatial characterization of rainfall in the Upper Blue Nile Basin are presented. Frequency analysis was performed on monthly basin rainfall. Monthly basin average rainfall data were computed from a network of 32 gauges with varying lengths of records. Monthly rainfall probability distribution varies from month to month fitting Gamma‐2, Normal, Weibull and Log‐Normal distributions. The January, July, October and November basin rainfall fit the Gamma‐2 probability distribution. The February, June and December ones fit Weibull distribution. The March, April, May and August rainfall fit Normal distribution. The September rainfall fits Log‐Normal distribution. Upper Blue Nile Basin is relatively wet with a mean annual rainfall of 1423 mm (1960–2002) with a standard deviation of 125 mm. The annual rainfall has a Normal probability distribution. The 100‐year‐drought basin annual rainfall is 1132 mm and the 100‐year‐wet basin annual rainfall is 1745 mm. The dry season is from November through April. The wet season runs from June through September with 74% of the annual rainfall. October and May are transition months. Monthly and annual rainfalls for return periods 2‐, 5‐, 10‐, 25‐, 50‐ and 100‐year dry and wet patterns are presented. Spatial distribution of annual rainfall over the basin is mapped and shows high variation with the southern tip receiving as high as 2049 mm and the northeastern tip as low as 794 mm annual average rainfall. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
Huai River Basin, as the sixth largest river basin in China, has a high‐regulated river system and has been facing severe water problems. In this article, the changing patterns of runoff and precipitation at 10 hydrological stations from 1956 to 2000 on the highly regulated river (Shaying River) and less‐regulated river (Huai River) in the basin are evaluated at the monthly, seasonal and annual scales using the Mann–Kendall test and simple linear regression model. The results showed that: (1) No statistically significant trends of precipitation in the upper and middle Huai River Basins were detected at the annual scale, but the trend of annual runoff at Baiguishan, Zhoukou and Fuyang stations in Shaying River decreased significantly, whereas the others were not. Moreover, the decreasing trends of runoff for most months were significant in Shaying River, although the trend of monthly precipitation decreased significantly only in April in the whole research area and the number of months in the dry season having significantly decreasing trends in runoff was more than that in the wet season. (2) The rainfall–runoff relationship was significant in both highly regulated river and less‐regulated river. In regulated river, the reservoirs have larger regulation capacity than the floodgates and thus have the smaller correlation coefficient and t‐value. In Huai River, the correlation coefficients decreased from upper stream to downstream. (3) The regulation of dams and floodgates for flood control and water supply was the principal reason for the decreasing runoff in Huai River Basin, although the decreasing precipitation in April in this basin was statistically significant. The findings are useful for recognizing hydrology variation and will provide scientific foundation to integrated water resources management in Huai River Basin. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
Increasing population and intensification of agriculture increase erosion rates and often result in severe land degradation and sedimentation of reservoirs. Finding effective management practices to counteract the increasing sediment load is becoming increasingly urgent especially in the Ethiopian highlands where the construction of the hydroelectric Grand Renaissance Dam on the Blue Nile is underway. In this paper, we examine the results of 9 years of a watershed experiment in which discharge and sediment losses were observed in the 113 ha Anjeni watershed of the Blue Nile Basin. The study period encompasses conditions before, during, and after the installation of graded Fanya‐Juu (“throw uphill” bunds) soil and water conservation practices (SWCP), which had the ultimate goal of creating terraces. We use a saturation‐excess runoff model named the parameter‐efficient distributed model as a mathematical construct to relate rainfall with discharge and sediment losses at the outlet. The parameter‐efficient distributed model is based on landscape units in which the excess rainfall becomes direct runoff or infiltrates based on topographic position or hardpan characteristics. Deviations in this rainfall–discharge–sediment loss relationship are ascribed to the changes in infiltration characteristics caused by SWCPs on the hillslopes. With this technique, we found that in the Anjeni basin, the Fanya‐Juu SWCPs are only effective in increasing the infiltration and thereby reducing the direct runoff and sediment concentrations in the first 5 years. At the end of the 9‐year observation period, the direct runoff and sediment concentrations were barely reduced compared to the levels before SWCP were installed. In addition, we found that the model structure based on landscape units was able to represent the varying runoff and erosion processes during the 9 years well by varying mainly the portion of degraded land (and thereby representing the effectiveness of the Fanya‐Juu to reduce runoff by increasing infiltration).  相似文献   

6.
A rainfall‐runoff model based on an artificial neural network (ANN) is presented for the Blue Nile catchment. The best geometry of the ANN rainfall‐runoff model in terms of number of hidden layers and nodes is identified through a sensitivity analysis. The Blue Nile catchment (about 300 000 km2) in the Nile basin is selected here as a case study. The catchment is classified into seven subcatchments, and the mean areal precipitation over those subcatchments is computed as a main input to the ANN model. The available daily data (1992–99) are divided into two sets for model calibration (1992–96) and for validation (1997–99). The results of the ANN model are compared with one of physical distributed rainfall‐runoff models that apply hydraulic and hydrologic fundamental equations in a grid base. The results over the case study area and the comparative analysis with the physically based distributed model show that the ANN technique has great potential in simulating the rainfall‐runoff process adequately. Because the available record used in the calibration of the ANN model is too short, the ANN model is biased compared with the distributed model, especially for high flows. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
A study was carried out to investigate variability in long term hydro-climatic extremes in the Lake Victoria basin, East Africa. The study aimed at determining whether the long term historical changes in frequency and magnitude of hydro-climatic extremes are statistically significant, to give more light on the differentiation of climate variability from climate change. Long term extremes for 22 rainfall and 10 river flow gauge stations were examined. The hydro-climatic extremes were aggregated at levels from daily, decadal, to monthly scales defined for two wet seasons in the area, the long rainy season extending from March to May (MAM) and the short rainy season extending from October to December (OND), and time slices of 10 years using a sliding window approach. An empirical statistical technique based on Quantile Perturbation Method (QPM) was used. Quantile perturbations that represent empirical changes for precipitation and river flow extremes were derived. Significant decreasing trends in precipitation were observed in the 1930s, 1970s and 1980s, while significant increasing trends were common in the 1960s, late 1980s, and 1990s to the most recent years (2000–2006). In general, significant trends were dominant in the OND compared to MAM season for precipitation and river flow extremes. Results indicated further that there are differences in geographic location of significant trends in the hydro-climatic variables investigated implying that impacts are not spatially coherent. Areas with significant trends appeared to be concentrated in the North to North eastern parts compared to those in the southern parts of the basin.  相似文献   

8.
The co-variation of rainfall and flow was assessed in four selected catchments of the River Nile which has two main sources including the White Nile (in the Equatorial region) and the Blue Nile (from the Ethiopian highlands). The selected catchments included Kyoga and Kagera (from the Equatorial region), as well as Blue Nile and Atbara (in Sudan and Ethiopia). In each catchment, the flow-rainfall co-variation was investigated at both seasonal and annual time scales. To explain aggregated variation at larger temporal scale while investigating the possible change in catchment behavior, which may interfere with the flow-rainfall relationship, rainfall-runoff modeling was done at daily time scale using data (falling within the period 1949–2003) from Kagera and Blue Nile i.e. the major catchment of each region where the River Nile emanates. Correlation analysis was conducted to assess how well the variation of flow and that of catchment-wide rainfall resonate. The co-occurrence of the changes in observed and simulated overland flow was examined using the quantile perturbation method (QPM). Trends in the model residuals were detected using the Mann–Kendal (MK) and cumulative rank difference (CRD) tests. The null hypothesis H 0 (no correlation between rainfall and flow) was rejected at the significance level α of 5% for all the selected catchments. The temporal changes in terms of the QPM anomalies for both the observed and simulated flow were in a close agreement. The evidence to reject the H 0 (no trend in the model residuals) was generally statistically insufficient at α = 5% for all the models and selected catchments considering both the MK and CRD tests. These results indicate that change in catchment behavior due to anthropogenic influence in the Nile basin over the selected time period was minimal. Thus, the overall rainfall-runoff generation processes of the catchments did not change in a significant way over the selected data period. The temporal flow variation could be attributed mainly to the rainfall variation.  相似文献   

9.
Abstract

Abstract Monthly precipitation and temperature trends of 51 stations in the Yangtze basin from 1950–2002 were analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation and temperature data. Significant positive and negative trends at the 90, 95 and 99% significance levels were detected. The monthly mean temperature, precipitation, summer precipitation and monthly mean runoff at Yichang, Hankou and Datong stations were analysed. The results indicate that spatial distribution of precipitation and temperature trends is different. The middle and lower Yangtze basin is dominated by upward precipitation trend but by somewhat downward temperature trend; while downward precipitation trend and upward temperature trend occur in the upper Yangtze basin. This is because increasing precipitation leads to increasing cloud coverage and, hence, results in decreasing ground surface temperature. Average monthly precipitation and temperature analysis for the upper, middle and lower Yangtze basin, respectively, further corroborate this viewpoint. Analysis of precipitation trend for these three regions and of runoff trends for the Yichang, Hankou and Datong stations indicated that runoff trends respond well to the precipitation trends. Historical flood trend analysis also shows that floods in the middle and lower Yangtze basin are in upward trend. The above findings indicate that the middle and lower Yangtze basin is likely to face more serious flood disasters. The research results help in further understanding the influence of climatic changes on floods in the Yangtze basin, providing scientific background for the flood control activities in large catchments in Asia.  相似文献   

10.
Abstract

An integrated model, combining a surface energy balance system, an LAI-based interception model and a distributed monthly water balance model, was developed to predict hydrological impacts of land-use/land-cover change (LUCC) in the East River basin, China, with the aid of GIS/RS. The integrated model is a distributed model that not only accounts for spatial variations in basin terrain, rainfall and soil moisture, but also considers spatial and temporal variation of vegetation cover and evapotranspiration (ET), in particular, thus providing a powerful tool for investigating the hydrological impact of LUCC. The model was constructed using spatial data on topography, soil types and vegetation characteristics together with time series of precipitation from 170 stations in the basin. The model was calibrated and validated based on river discharge data from three stations in the basin for 21 years. The calibration and validation results suggested that the model is suitable for application in the basin. The results show that ET has a positive relationship with LAI (leaf area index), while runoff has a negative relationship with LAI in the same climatic zone that can be described by the surface energy balance and water balance equation. It was found that deforestation would cause an increase in annual runoff and a decrease in annual ET in southern China. Monthly runoff for different land-cover types was found to be inversely related to ET. Also, for most of the scenarios, and particularly for grassland and cropland, the most significant changes occurred in the rainy season, indicating that deforestation would cause a significant increase in monthly runoff in that season in the East River basin. These results are important for water resources management and environmental change monitoring.
Editor Z.W. Kundzewicz  相似文献   

11.
The objective of this study was to quantify the impacts of land use/land cover (LULC) change on the hydrology of the Jedeb, an agricultural dominated mesoscale catchment, in the Abay/Upper Blue Nile basin, Ethiopia. Two methods have been used. First, the trends of certain daily flow variability parameters were evaluated to detect statistical significance of the change of the hydrologic response. Second, a conceptual monthly hydrological model was used to detect changes in the model parameters over different periods to infer LULC change. The results from the statistical analysis of the daily flows between 1973 and 2010 reveal a significant change in the response of the catchment. Peak flow is enhanced, i.e. response appears to be flashier. There is a significant increase in the rise and fall rates of the flow hydrograph, as well as the number of low‐flow pulses below a threshold level. The discharge pulses show a declining duration with time. The model result depicts a change in model parameters over different periods, which could be attributed to an LULC change. The model parameters representing soil moisture conditions indicated a gradual decreasing trend, implying limited storage capacity likely attributed to increasing agricultural farming practices in the catchment. This resulted in more surface runoff and less infiltration into the soil layers. The results of the monthly flow duration curve analysis indicated large changes of the flow regime. The high flow has increased by 45% between the 1990s and 2000s, whereas the reduction in low flows was larger: a 15% decrease between 1970s and 1980s, 39% between 1980s and 1990s and up to 71% between 1990s and 2000s. These results, could guide informed catchment management practices to reduce surface runoff and augment soil moisture level in the Jedeb catchment. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

12.
Climate change is expected to affect air temperature and watershed hydrology, but the degree to which these concurrent changes affect stream temperature is not well documented in the tropics. How stream temperature varies over time under changing hydrologic conditions is difficult to isolate from seasonal changes in air temperature. Groundwater and bank storage contributions to stream flow (i.e., base flow [BF]) buffer water temperatures against seasonal and daily fluctuations in solar radiation and air temperature, whereas rainfall‐driven runoff produces flooding events that also influence stream temperature. We used a space‐for‐time substitution to examine how shifts in BF and runoff alter thermal regimes in streams by analyzing hydrological and temperature data collected from similar elevations (400–510 m above sea level) across a 3,500‐mm mean annual rainfall gradient on Hawai'i Island. Sub‐daily water temperature and stream flow gathered for 3 years were analyzed for daily, monthly, and seasonal trends and compared with air temperature measured at multiple elevations. Results indicate that decreases in median BF increased mean, maximum, and minimum water temperatures as well as daily temperature range. Monthly and daily trends in stream temperature among watersheds were more pronounced than air temperature, driven by differences in groundwater inputs and runoff. Stream temperature was strongly negatively correlated to BF during the dry season but not during the wet season due to frequent wet season runoff events contributing to total flow. In addition to projected increases in global air temperature, climate driven shifts in rainfall and runoff are likely to affect stream flow and groundwater recharge, with concurrent influences on BF resulting in shifts in water temperature that are likely to affect aquatic ecosystems.  相似文献   

13.
Water resources and soil erosion are the most important environmental concerns in the Yangtze River basin, where soil erosion and sediment yield are closely related to rainfall erosivity. The present study explores the spatial and temporal changing patterns of the rainfall erosivity in the Yangtze River basin of China during 1960–2005 at annual, seasonal and monthly scales. The Mann–Kendall test is employed to detect the trends during 1960–2005, and the T test is applied to investigate possible changes between 1991–2005 and 1960–1990. Meanwhile the Rescaled Range Analysis is used for exploring future trend of rainfall erosivity. Moreover the continuous wavelet transform technique is using studying the periodicity of the rainfall erosivity. The results show that: (1) The Yangtze River basin is an area characterized by uneven spatial distribution of rainfall erosivity in China, with the annual average rainfall erosivity range from 131.21 to 16842 MJ mm ha?1 h?1. (2) Although the directions of trends in annual rainfall erosivity at most stations are upward, only 22 stations have significant trends at the 90 % confidence level, and these stations are mainly located in the Jinshajiang River basin and Boyang Lake basin. Winter and summer are the seasons showing strong upward trends. For the monthly series, significant increasing trends are mainly found during January, June and July. (3) Generally speaking, the results detected by the T test are quite consistent with those detected by the Mann–Kendall test. (4) The rainfall erosivity of Yangtze River basin during winter and summer will maintain a detected significant increasing trend in the near future, which may bring greater risks to soil erosion. (5) The annual and seasonal erosivity of Yangtze River basin all have one significant periodicity of 2–4 years.  相似文献   

14.
The low and high flow characteristic of the Blue Nile River (BNR) basin is presented. The study discusses low and high flow, flow duration curve (FDC) and trend analysis of the BNR and its major tributaries. Different probability density functions were fitted to better describe the low and high flows of the BNR and major tributaries in the basin. Wavelet analysis was used in understanding the variance and frequency‐time localization and detection of dominant oscillations in rainfall and flow. FDCs were developed, and low flow (below 50% exceedance) and high flow (over 75% exceedance) of the curves were analysed and compared. The Gravity Recovery and Climate Experiment (GRACE) satellite‐based maps of monthly changes in gravity converted to water equivalents from 2003 to 2006 for February, May and September showed an increase in the moisture influx in the BNR basin for the month of September, and loss of moisture in February and May. It was also shown that 2004 and 2005 were drier with less moisture influx compared to 2003 and 2006. On the basis of the Kolmogorov‐Smirnov, Anderson‐Darling and Chi‐square tests, Gen. Pareto, Frechet 3P, Log‐normal, Log‐logistics, Fatigue Life and Phased Bi‐Weibull distributions best describe the low and high flows within the BNR basin. This will be beneficial in developing flow hydrographs for similar ungauged watersheds within the BNR basin. The below 50% and above 75% exceedance on the FDC for five major rivers in addition to the BNR showed different characteristics depending on size, land cover, topography and other factors. The low flow frequency analysis of the BNR at Bahir Dar showed 0·55 m3/s as the monthly low flow with recurrence interval of 10 years. The wavelet analysis of the rainfall (at Bahir Dar and basin‐wide) and flows at three selected stations shows inter‐ and intra‐annual variability of rainfall and flows at various scales. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

15.
The runoff in Songhuajiang River catchment has experienced a decreasing trend during the second half of the 20th century. Serially complete daily rainfall data of 42 rainfall stations from 1959 to 2002 and daily runoff data of five meteorological stations from 1953 to 2005 were obtained. The Mann–Kendall trend test and the sequential version of Mann–Kendall test were employed in this study to test the monthly and annual trends for both rainfall and runoff, to determine the start point of abrupt runoff declining, and to identify the main driving factors of runoff decline. The results showed an insignificant increasing trend in rainfall but a significant decreasing trend in runoff in the catchment. For the five meteorological stations, abrupt runoff decline occurred during 1957–1963 and the middle 1990s. Through Mann–Kendall comparisons for the area‐rainfall and runoff for the two decreasing periods, human activity, rather than climatic change, is identified as the main driving factor of runoff decline. Analysis of land use/cover shows that farmland is most related with runoff decline among all the land use/cover change in Nenjiang catchment. From 1986 to 1995, the area of farmland increased rapidly from 6.99 to 7.61 million hm2. Hydraulic engineering has a significant influence on the runoff decline in the second Songhuajiang catchment. Many large‐scale reservoirs and hydropower stations have been built in the upstream of the Second Songhuajiang and lead to the runoff decline. Nenjiang and the Second Songhuajiang are the two sources of mainstream of Songhuajiang. Decreased runoff in these two sub‐catchments then results in runoff decrease in mainstream of Songhuajiang catchment. It is, therefore, concluded that high percent agricultural land and hydraulic engineering are the most probable driving factors of runoff decline in Songhuajiang River catchment, China.  相似文献   

16.
Climatic and hydrological changes will likely be intensified in the Upper Blue Nile (UBN) basin by the effects of global warming. The extent of such effects for representative concentration pathways (RCP) climate scenarios is unknown. We evaluated projected changes in rainfall and evapotranspiration and related impacts on water availability in the UBN under the RCP4.5 scenario. We used dynamically downscaled outputs from six global circulation models (GCMs) with unprecedented spatial resolution for the UBN. Systematic errors of these outputs were corrected and followed by runoff modelling by the HBV (Hydrologiska ByrånsVattenbalansavdelning) model, which was successfully validated for 17 catchments. Results show that the UBN annual rainfall amount will change by ?2.8 to 2.7% with a likely increase in annual potential evapotranspiration (in 2041–2070) for the RCP4.5 scenario. These changes are season dependent and will result in a likely decline in streamflow and an increase in soil moisture deficit in the basin.  相似文献   

17.
《Journal of Hydrology》2006,316(1-4):233-247
The annual water budget of Lake Tana is determined from estimates of runoff, rainfall on the lake, measured outflow and empirically determined evaporation. Simulation of lake level variation (1960–1992) has been conducted through modeling at a monthly time step. Despite the ±20% rainfall variations in the Blue Nile basin in the last 50 years, the lake level remained regular. A preliminary analysis of the sensitivity of level and outflow of the lake suggests that they are controlled more by variation in rainfall than by basin-scale forcing induced by human activities. The analysis shows that a drastic (40–45%) and sustained (7–8 years) rainfall reduction is required to change the lake from out flowing to terminal (cessation of outflow). However, the outflow from the lake shows significant variation responding to the rainfall variations. Unlike the terminal lakes in the Ethiopian rift valley or the other large lakes of Tropical Africa, at its present hydrologic condition, the Lake Tana level is less sensitive to rainfall variation and changes in catchment characteristics.  相似文献   

18.
An analysis of spatial and temporal trends of precipitation in Beijiang River basin, Guangdong Province, China during 1959–2003 was performed using 17 time series (including monthly, annual, wet season, dry season, early flood period and late flood period totals) both on station based and sub‐basin based data sets. Two nonparametric methods (Mann–Kendall and Sen's T) were used for data analysis. The results showed that (1) downward trends of temporal distribution were mostly detected during the early flood period, especially in May, while upward trends were observed in July and the dry season; (2) downward trends of spatial distribution were mostly detected in the southern Beijiang River basin, while upward trends were observed north of this area. Our results indicated a delayed rainy season and a northward trend of the precipitation belt compared to recent years. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

19.
ABSTRACT

The suspended sediment rating curves for six stations on four rivers in western and northern Greece are investigated. For each station the suspended sediment load is a power function of the water discharge, which may be distinguished according to wet and dry seasons; the latter yields higher sediment loads for a given discharge than the former. This is due to the higher erosivity of dry season rainfall compared to wet season rainfall producing the same runoff. All rating curve exponents b lie in the range 2.5–3.5 for the wet and 2.0–3.0 for the dry season and are related to the constants a of the curves by empirical equations. The variation in a and b is explained in terms of the annual precipitation and area of the basin, the hypsometric fall, the main channel length, and the average bedslope of the river from the basin divide to the station, through empirical relationships, which also permit the prediction of rating curves for ungauged basins.  相似文献   

20.
Seasonal and annual trends of changes in rainfall, rainy days, heaviest rain and relative humidity have been studied over the last century for nine different river basins in northwest and central India. The majority of river basins have shown increasing trends both in annual rainfall and relative humidity. The magnitude of increased rainfall for considered river basins varied from 2–19% of mean per 100 years. The maximum increase in rainfall is observed in the Indus (lower) followed by the Tapi river basin. Seasonal analysis shows maximum increase in rainfall in the post‐monsoon season followed by the pre‐monsoon season. There were least variations in the monsoon rainfall during the last century and winter rainfall has shown a decreasing trend. Most of the river basins have experienced decreasing trends in annual rainy days with a maximum decrease in the Mahanadi basin. The heaviest rain of the year has increased from 9–27 mm per 100 years over different river basins with a maximum of 27 mm for the Brahamani and Subaranrekha river basins. A combination of increase in heaviest rainfall and reduction in the number of rainy days suggest the possibility of increasing severity of floods. Such information is useful in the planning, development and management of water resources in the study area. Further, the majority of river basins have also experienced an increasing trend in relative humidity both on seasonal and annual scales. An increase in annual mean relative humidity for six river basins has been found in the range of 1–18% of mean per 100 years, while a decrease for three river basins from ? 1 to ? 13% of mean per 100 years was observed, providing a net increase in the study area by 2·4% of mean per 100 years. It is understood that an increase in areal extent of vegetation cover as well as rainfall over the last century has increased the moisture in the atmosphere through enhanced evapotranspiration, which in turn has increased the relative humidity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

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