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1.
Climatic change impacts on the ecohydrology of Mediterranean watersheds   总被引：2，自引：0，他引：2  
Impact of climate change on ecohydrologic processes of Mediterranean watersheds are significant and require quick action toward improving adaptation and management of fragile system. Increase in water shortages and land use can alter the water balance and ecological health of the watershed systems. Intensification of land use, increase in water abstraction, and decline in water quality can be enhanced by changes in temperature and precipitation regimes. Ecohydrologic changes from climatic impacts alter runoff, evapotranspiration, surface storage, and soil moisture that directly affect biota and habitat of the region. This paper reviews expected impacts of climatic change on the ecohydrology of watershed systems of the Mediterranean and identifies adaptation strategies to increase the resilience of the systems. A spatial assessment of changes in temperature and precipitation estimates from a multimodel ensemble is used to identify potential climatic impacts on watershed systems. This is augmented with literature on ecohydrologic impacts in watershed systems of the region. Hydrologic implications are discussed through the lens of geographic distribution and upstream-downstream dynamics in watershed systems. Specific implications of climatic change studied are on runoff, evapotranspiration, soil moisture, lake levels, water quality, habitat, species distribution, biodiversity, and economic status of countries. It is observed that climatic change can have significant impacts on the ecohydrologic processes in the Mediterranean watersheds. Vulnerability varied depending on the geography, landscape characteristics, and human activities in a watershed. Increasing the resilience of watershed systems can be an effective strategy to adapt to climatic impacts. Several strategies are identified that can increase the resilience of the watersheds to climatic and land use change stress. Understanding the ecohydrologic processes is vital to development of effective long-term strategies to improve the resilience of watersheds. There is need for further research into ecohydrologic dynamics at multiple scales, improved resolution of climatic predictions to local scales, and implications of disruptions on regional economies.  相似文献   

2.
The variability of the main components of the annual water balance (precipitation, evaporation, glacial alimentation, and dynamic water reserves in the basin) for 1935–1990 is, for the first time, determined for the area where the Zeravshan runoff is formed, higher than hydrological post Dupuli is located. Long-term data on the annual Zeravshan River runoff from an area of 10 200 km2 were derived from the measurements at Dupuli hydrological post. The other water balance components were determined with the help of computation methods. Comparison of the measured and calculated volumes of the annual runoff demonstrated that a relative difference between them is systematic, and as a whole for a computation period it is in the interval from ?0.31 to ?4.78%. The annual balance of accumulation and thawing of solid precipitation on glaciers and in the extraglacial area is also determined in the Zeravshan River basin. A new method for computing and mapping spatial variability of the maximum snowline altitude is developed.  相似文献   

3.
Pacific Northwest (PNW) hydrology is particularly sensitive to changes in climate because snowmelt dominates seasonal runoff, and temperature changes impact the rain/snow balance. Based on results from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), we updated previous studies of implications of climate change on PNW hydrology. PNW 21st century hydrology was simulated using 20 Global Climate Models (GCMs) and 2 greenhouse gas emissions scenarios over Washington and the greater Columbia River watershed, with additional focus on the Yakima River watershed and the Puget Sound which are particularly sensitive to climate change. We evaluated projected changes in snow water equivalent (SWE), soil moisture, runoff, and streamflow for A1B and B1 emissions scenarios for the 2020s, 2040s, and 2080s. April 1 SWE is projected to decrease by approximately 38–46% by the 2040s (compared with the mean over water years 1917–2006), based on composite scenarios of B1 and A1B, respectively, which represent average effects of all climate models. In three relatively warm transient watersheds west of the Cascade crest, April 1 SWE is projected to almost completely disappear by the 2080s. By the 2080s, seasonal streamflow timing will shift significantly in both snowmelt dominant and rain–snow mixed watersheds. Annual runoff across the State is projected to increase by 2–3% by the 2040s; these changes are mainly driven by projected increases in winter precipitation.  相似文献   

4.
Precipitation from the Eastern Sierra Nevada watersheds of Owens Lake and Mono Lake is one of the main water sources for Los Angeles’ over 4 million people, and plays a major role in the ecology of Mono Lake and of these watersheds. We use the Variable Infiltration Capacity (VIC) hydrologic model at daily time scale, forced by climate projections from 16 global climate models under greenhouse gas emissions scenarios B1 and A2, to evaluate likely hydrologic responses in these watersheds for 1950–2099. Comparing climate in the latter half of the 20th Century to projections for 2070–2099, we find that all projections indicate continued temperature increases, by 2–5 °C, but differ on precipitation changes, ranging from ?24 % to +56 %. As a result, the fraction of precipitation falling as rain is projected to increase, from a historical 0.19 to a range of 0.26–0.52 (depending on the GCM and emission scenario), leading to earlier timing of the annual hydrograph’s center, by a range of 9–37 days. Snowpack accumulation depends on temperature and even more strongly on precipitation due to the high elevation of these watersheds (reaching 4,000 m), and projected changes for April 1 snow water equivalent range from ?67 % to +9 %. We characterize the watershed’s hydrologic response using variables integrated in space over the entire simulated area and aggregated in time over 30-year periods. We show that from the complex dynamics acting at fine time scales (seasonal and sub-seasonal) simple dynamics emerge at this multi-year time scale. Of particular interest are the dynamic effects of temperature. Warming anticipates hydrograph timing, by raising the fraction of precipitation falling as rain, reducing the volume of snowmelt, and initiating snowmelt earlier. This timing shift results in the depletion of soil moisture in summer, when potential evapotranspiration is highest. Summer evapotranspiration losses are limited by soil moisture availability, and as a result the watershed’s water balance at the annual and longer scales is insensitive to warming. Mean annual runoff changes at base-of-mountain stations are thus strongly determined by precipitation changes.  相似文献   

5.
The global energy balance from a surface perspective   总被引：1，自引：1，他引：0  
In the framework of the global energy balance, the radiative energy exchanges between Sun, Earth and space are now accurately quantified from new satellite missions. Much less is known about the magnitude of the energy flows within the climate system and at the Earth surface, which cannot be directly measured by satellites. In addition to satellite observations, here we make extensive use of the growing number of surface observations to constrain the global energy balance not only from space, but also from the surface. We combine these observations with the latest modeling efforts performed for the 5th IPCC assessment report to infer best estimates for the global mean surface radiative components. Our analyses favor global mean downward surface solar and thermal radiation values near 185 and 342 Wm?2, respectively, which are most compatible with surface observations. Combined with an estimated surface absorbed solar radiation and thermal emission of 161 and 397 Wm?2, respectively, this leaves 106 Wm?2 of surface net radiation available globally for distribution amongst the non-radiative surface energy balance components. The climate models overestimate the downward solar and underestimate the downward thermal radiation, thereby simulating nevertheless an adequate global mean surface net radiation by error compensation. This also suggests that, globally, the simulated surface sensible and latent heat fluxes, around 20 and 85 Wm?2 on average, state realistic values. The findings of this study are compiled into a new global energy balance diagram, which may be able to reconcile currently disputed inconsistencies between energy and water cycle estimates.  相似文献   

6.
The spatio-temporal variations of the water budget components in the Amazon region are investigated by using a combination of hydrometeorological observations and moisture fluxes derived from the NCEP/NCAR reanalyses, for the period 1970–1999. The key new finding of this study identifies the major differences in the water balance characteristics and variability between the northern and southern parts of the basin. Our results show that there is a seasonality and interannual variability of the water balance that varies across the basin. At interannual time scales, anomalies in the water balance components in the northern Amazon region show relatively stronger links with tropical Pacific interannual variability. Over the entire region, precipitation exceeds evaporation and the basin acts as a sink of moisture (P>E). However, on some occasions the basin can act as a source for moisture (P<E) under extreme conditions, such as those related to deficient rainfall in northern Amazonia during the strong El Niño of 1983. Our estimates of the Amazon regions water balance do not show a closure of the budget, with an average imbalance of almost 50%, suggesting that some of the moisture that converges in the Amazon region is not accounted for. The imbalance is larger over the southern Amazon region than over the northern region, and it also exhibits interannual variability. Large uncertainties are detected in the evaporation and moisture-convergence fields derived from the reanalyses, and in the case of evaporation it can be as large as 10–20% when compared with the few field observations across the basin. Observed precipitation fields derived from station data and from grid-box products also show some discrepancies due to sampling problems and interpolation techniques. The streamflow observed at the mouth of the river is obtained after corrections on the series observed taken at a gauging site almost 200 km inland. However, variability in the evaporation, moisture convergence, and observed rainfall and runoff matches quite well.  相似文献   

7.
Results of simulation of radiation, cloud cover, surface air temperature, sea-level pressure, and hydrological regime components for Russia with the help of an ensemble of CMIP3 global climate models is analyzed. Despite a large spread among the models, the CMIP3 AOGCM ensemble simulations of the key characteristics of the observed surface climate agree well with observations, anyway in averaging over areas of vast regions, from watersheds of large rivers to the whole of Russia. These means (ensemble-and area-averaged values) often fall into the range of estimates derived from observations. This suggests the existence of uncertainty in the estimates obtained from simulations as well as from observational data. Comparison of different-generation models demonstrates a gradual improvement of the AOGCM simulation of surface climate characteristics. In general, the averaging over the CMIP3 AOGCM ensemble allows us to state that the ensemble is suitable for estimates of future climate changes.  相似文献   

8.
This paper evaluates the performance of eight state-of-art IPCC-AR4 coupled atmosphere-ocean general circulation models in their representation of regional characteristics of atmospheric water balance over South Asia. The results presented here are the regional climate change scenarios of atmospheric water balance components, precipitation, moisture convergence and evaporation (P, C and E) up to the end of the twenty-second century based on IPCC AR4 modelling experiments conducted for (A1B) future greenhouse gas emission scenario. The AOGCMs, despite their relatively coarse resolution, have shown a reasonable skill in depicting the hydrological cycle over the South Asian region. However, considerable biases do exist with reference to the observed atmospheric water balance and also inter-model differences. The monsoon rainfall and atmospheric water balance changes under A1B scenario are discussed in detail. Spatial patterns of rainfall change projections indicate maximum increase over northwest India in most of the models, but changes in the atmospheric water balance are generally widespread over South Asia. While the scenarios presented in this study are indicative of the expected range of rainfall and water balance changes, it must be noted that the quantitative estimates still have large uncertainties associated with them.  相似文献   

9.
The purpose of this paper is to analyse the regional impact of recent climate change on the water resources in southern France. We produced spatial reconstructions of the monthly evolutions of temperature, precipitation and water discharge in 15 watersheds of six coastal river basins and examined the major changes based on trend analysis for the last 40 years. In this part of the Mediterranean, the general warming trend was strongly enhanced by changes in the atmospheric circulation patterns, characterized by a northward extension of the subtropical high pressure domain during spring and summer. During these seasons, monthly warming rates could achieve almost twice the mean annual warming rates. Although annual precipitation did not follow clear trends, water discharge significantly decreased in one third of the watersheds and accounted for an estimated 20% reduction of the water resources in this region. This concerns both the highest and lowest watersheds. In the former, the reduction is likely the result of a temperature induced switch of snowfall to rainfall at high altitudes. In the latter, the reduction of discharge seems to come from lower groundwater levels, which may be related to the temperature increase too, but also have other origins. The recent climatic evolution is consistent with most modelling simulations for the future, indicating that the reduction of the water resources will hold on, probably still enhanced by decreases in precipitation.  相似文献   

10.
Summary ?This paper deals with variations and trends in some components of the water balance: the soil water content; evaporation loss from the soil (from the surface and underlying layers); transpiration; ground water recharge and runoff. These components are calculated by means of the Palmer procedure. This analysis is based on data from Osijek, Croatia from this century (1900–1995). Besides the meteorological input parameters necessary for the water balance calculations, i.e. precipitation, temperature and relative humidity, the pedological characteristics of this area have also been taken into account. Fluctuations have been considered by means of the 11-year binomial filtered series and linear trends were tested by means of the Mann-Kendall rank test. For a closer look on the trends of water balance components, a progressive analysis of the time series was performed, too. The results show a significant increase in potential evapotranspiration and evapotranspiration and decrease in runoff and soil water content has occurred during the century. Received February 22, 1999/Revised August 3, 1999  相似文献   

11.
Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration (PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year?1, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1–16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by ?10.2 to ?2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed.  相似文献   

12.
The data on the radiation balance of underlying surface, its components, and main factors defining their variations are systematized and generalized for 50 years (1958–2007) on the basis of continuous observations at the Meteorological Observatory of the Moscow State University. The climatic norms of radiation balance are obtained and its variability (diurnal, annual, and interannual) limits are estimated. The correlation dependences between its main components and factors influencing their variability are obtained and the probability of one or another diurnal radiation balance sum during the year is determined. The existence is demonstrated of the tendency toward the increase in the absorbed, effective, and atmospheric back radiation and terrestrial radiation balance mostly pronounced in the nighttime in winter months.  相似文献   

13.
Variations of global evapotranspiration (ET) and fresh water discharge from land to oceans (D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation (E o ). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation.  相似文献   

14.
Abstract

Second generation land surface schemes are the subject of much development activity among atmospheric modellers. This work is aimed at, among other things, improving the representation of the soil water balance in order to simulate, more properly, exchanges with the atmosphere and to permit the use of model output to generate streamflow for model validation. The Canadian development program is centred on CLASS, the Canadian Land Surface Scheme, developed at Environment Canada. This paper focuses on the improvement of hydrology in CLASS. This was accomplished by designing a two‐way interface to WATFLOOD, a distributed hydrologic model developed at the University of Waterloo. The two models share many features, which facilitated the coupling procedure.

The interface retains the three‐layer vertical moisture budget representation in CLASS but adds three horizontal runoff possibilities. Runoff from the surface water follows Manning's equation for overland flow. Interflow is generated from the near‐surface soil layer using a parametrization of Richard's equation and base flow is produced by Darcian flow from the bottom of layer 3. An approximation of the internal topography of grid elements is used to supply horizontal gradients for the runoff components.

Tests are in progress in four Canadian study areas. Initial results are presented for the summer of 1993 for the Saugeen River in southwestern Ontario. The new scheme produces realistic hydrographs, whereas the old scheme did not. Bare ground evaporation is reduced by about 17% as a consequence of reduced water availability in layer 1. Evapotranspiration is not affected because the rooting depth extends into layer 3, in which soil moisture does not change appreciably with the new scheme. These results suggest that the new scheme improves the representation of streamflow in WATFLOOD/CLASS and of the soil moisture budget in CLASS. Work is in progress to validate this result over basins, such as the BOREAS study watersheds, where both runoff and evapotranspiration measurements are available.  相似文献   

15.
基于全球2 894个流域的河川径流量、归一化植被指数（Normalized Differential Vegetation Index,NDVI）以及气温和降水量长期数据,发现年内月均径流量（MQ）呈上升、下降以及不显著变化趋势的流域比例分别为9.1%、12.4%和78.5%,年内最小月径流量（LQ）呈3种变化趋势的流域比例分别为24.1%、11.7%和64.2%,年内最大月径流量（HQ）呈3种变化趋势的流域比例分别为6.4%、13.6%和79.9%。在区域（大陆和纬度带）和全球尺度上,没有出现LQ下降和HQ上升变化趋势的现象,MQ下降与HQ下降联系在一起,MQ上升与LQ上升联系在一起,表明区域和全球尺度上水资源量及年内分配在过去60多年里是改善的。进一步分析发现,气候变化是导致水资源量和年内分配变化的主要因素。但与年内月极端径流量（LQ或HQ）变化不同的是,发生年内月极端径流量的月份大多发生了显著的改变,这个改变可能对社会和自然生态系统以及依靠自然节律的生产生活方式产生深远影响。  相似文献   

16.
River discharge forms a major freshwater input into the Arctic Ocean, and as such it has the potential to influence the oceanic circulation. As the hydrology of Arctic river basins is dominated by cryospheric processes such as snow accumulation and snowmelt, it may also be highly sensitive to a change in climate. Estimating the water balance of these river basins is therefore important, but it is complicated by the sparseness of observations and the large uncertainties related to the measurement of snowfalls. This study aims at simulating the water balance of the Barents Sea drainage basin in Northern Europe under present and future climate conditions. We used a regional climate model to drive a large-scale hydrological model of the area. Using simulated precipitation derived from a climate model led to an overestimation of the annual discharge in most river basins, but not in all. Under the B2 scenario of climate change, the model simulated a 25% increase in freshwater runoff, which is proportionally larger than the projected precipitation increase. As the snow season is 30–50 day shorter, the spring discharge peak is shifted by about 2–3 weeks, but the hydrological regime of the rivers remains dominated by snowmelt.  相似文献   

17.
Direct measurement of turbulent fluxes on a cruising ship   总被引：1，自引：0，他引：1  
The result of an attempt at the direct measurement of turbulent fluxes on the top of the mast of a cruising ship is presented. The three-dimensional components of wind relative to the ship measured by a sonic anemometer are corrected for ship motion; from these the fluxes of momentum, sensible heat and water vapor are computed using the outputs of a fine-wire thermocouple psychrometer. The observations were made by this method on the Northwestern Pacific. The results indicate that this technique is usable for determining the distribution of fluxes over the ocean.  相似文献   

18.
Energy balance closure for the LITFASS-2003 experiment   总被引：2，自引：1，他引：1  
In the first part, this paper synthesises the main results from a series of previous studies on the closure of the local energy balance at low-vegetation sites during the LITFASS-2003 experiment. A residual of up to 25% of the available energy has been found which cannot be fully explained either by the measurement uncertainty of the single components of the surface energy balance or by the length of the flux-averaging period. In the second part, secondary circulations due to heterogeneities in the surface characteristics (roughness, thermal and moisture properties) are discussed as a possible cause for the observed energy balance non-closure. This hypothesis seems to be supported from the fluxes derived from area-averaging measurement techniques (scintillometers, aircraft).  相似文献   

19.
植物对降水截留的研究进展   总被引：2，自引：0，他引：2       下载免费PDF全文
降水资源是植物生长发育和产量形成的主要水分来源,植物通过吸收土壤中的水分维持正常生长发育,降水不仅影响自然植物物种分布,也影响植物生产力。由于未考虑植物冠层对降水的截留作用,在水资源评估和农田水分平衡研究中往往高估降水作用,因此,讨论降水截留在水文生态学和农业气象学中均有重要意义。该文系统介绍降水截留的观测方法,包括间接测量法中各分量测定方法、直接测量法详细过程及应用各种方法需注意的问题;系统回顾有关森林和农作物对降水截留的研究成果;探讨在植物对降水截留研究中存在的主要问题:对截留概念的理解不同导致截留测定结果差异显著,没有完善的方法导致测定结果准确性不足,植物种植密度不同导致截留差异,降水强度不同导致截留差异,风速、植物形态结构、叶片表面特性等因素也会影响降水截留的大小。降水过程中植物叶面蒸发问题、降雪的截留问题、风的影响、研究尺度、研究方法以及综合模拟模型将是未来研究的重点和难点。  相似文献   

20.
The hydrological cycle can influence climate through a great variety of processes. A good representation of the hydrological cycle in climate models is therefore crucial. Attempts to analyse the global hydrological cycle are hampered by a deficiency of suitable observations, particularly over the oceans. Fully coupled general circulation models are potentially powerful tools in interpreting the limited observational data in the context of large-scale freshwater exchanges. We have looked at large-scale aspects of the global freshwater budget in a simulation, of over 1000 years, by the Hadley Centre coupled climate model (HadCM3). Many aspects of the global hydrological cycle are well represented, but the model hydrological cycle appears to be too strong, with overly large precipitation and evaporation components in comparison with the observational datasets we have used. We show that the ocean basin-scale meridional transports of freshwater come into near balance with the surface freshwater fluxes on a time scale of about 400 years, with the major change being a relative increase of freshwater transport from the Southern Ocean into the Atlantic Ocean. Comparison with observations, supported by sensitivity tests, suggests that the major cause of a drift to more saline condition in the model Atlantic is an overestimate of evaporation, although other freshwater budget components may also play a role. The increase in ocean freshwater transport into the Atlantic during the simulation, primarily coming from the overturning circulation component, which changes from divergent to convergent, acts to balance this freshwater budget deficit. The stability of the thermohaline circulation in HadCM3 may be affected by these freshwater transport changes and this question is examined in the context of an existing conceptual model.  相似文献   

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