Effects of vegetation cover on summer climate in China during 1982–2001     

Aziz Salim Habib  Xiaoling Chen  Jianya Gong  Li Zhang 《地球空间信息科学学报》2009,12(1):41-45

In this paper, we apply lagged correlation analysis to study the effects of vegetation cover on the summer climate in different zones of China, using NOAA/AVHRR normalized difference vegetation index (NDVI) data during the time period from 1982 to 2001 and climate data of 365 meteorological stations across China (precipitation from 1982 to 2001 and temperature from 1982 to 1998). The results show that there are positive correlations between spring NDVI and summer climate (temperature and precipitation) in most zones of China; these suggest that, when the vegetation cover increases, the summer precipitation will increase, and the lagged correlations show a significant difference between zones. The stronger correlations between NDVI in previous season and summer climate occur in three zones (Mid-temperate zone, Warm-temperate zone and Plateau climate zone), and this implies that vegetation changes have more sensitive feedback effects on climate in the three zones in China. Supported by the National 973 Program of China (No.2006CB701300), the National Natural Science Foundation of China (No.40721001), the Sino-Germany Joint Project (No. 2006DFB91920), the Open Fund of Shanghai Leading Academic Discipline Project (T0102) and the Open Fund of LIESMARS, Wuhan University.  相似文献   

Spatial patterns and trends of daily rainfall regime in Peninsular Malaysia during the southwest and northeast monsoons: 1975–2004     

Jamaludin Suhaila  S. M. Deni  Wan Zawiah Wan Zin  Abdul Aziz Jemain 《Meteorology and Atmospheric Physics》2010,106(1-2):1-18

Model precipitation can be produced implicitly through convective parameterization schemes or explicitly through cloud microphysics schemes. These two precipitation production schemes control the spatial and temporal distribution of precipitation and consequently can yield distinct vertical profiles of heating and moistening in the atmosphere. The partition between implicit and explicit precipitation can be different as the model changes resolutions. Within the range of mesoscale resolutions (about 20 km) and cumulus scale, hybrid solutions are suggested, in which cumulus convection parameterization is acting together with the explicit form of representation. In this work, it is proposed that, as resolution increases, the convective scheme should convert less condensed water into precipitation. Part of the condensed water is made available to the cloud microphysics scheme and another part evaporates. At grid sizes smaller than 3 km, the convective scheme is still active in removing convective instability, but precipitation is produced by cloud microphysics. The Eta model version using KF cumulus parameterization was applied in this study. To evaluate the quantitative precipitation forecast, the Eta model with the KF scheme was used to simulate precipitation associated with the South Atlantic Convergence Zone (SACZ) and Cold Front (CF) events. Integrations with increasing horizontal resolutions were carried out for up to 5 days for the SACZ cases and up to 2 days for the CF cases. The precipitation partition showed that most of precipitation was generated by the implicit scheme. As the grid size decreased, the implicit precipitation increased and the explicit decreased. However, as model horizontal resolution increases, it is expected that precipitation be represented more explicitly. In the KF scheme, the fraction of liquid water or ice, generated by the scheme, which is converted into rain or snow is controlled by a parameter S ₁. An additional parameter was introduced into KF scheme and the parameter acts to evaporate a fraction of liquid water or ice left in the model grid by S ₁ and return moisture to the resolved scale. An F parameter was introduced to combine the effects of S ₁ and S ₂ parameters. The F parameter gives a measure of the conversion of cloud liquid water or ice to convective precipitation. A function dependent on the horizontal resolution was introduced into the KF scheme to influence the implicit and explicit precipitation partition. The explicit precipitation increased with model resolution. This function reduced the positive precipitation bias at all thresholds and for the studied weather systems. With increased horizontal resolution, the maximum precipitation area was better positioned and the total precipitation became closer to observations. Skill scores for all events at different forecast ranges showed precipitation forecast improvement with the inclusion of the function F.  相似文献   

Spatial trends of dry spells over Peninsular Malaysia during monsoon seasons   总被引：1，自引：0，他引：1  

Sayang Mohd Deni  Jamaludin Suhaila  Wan Zawiah Wan Zin  Abdul Aziz Jemain 《Theoretical and Applied Climatology》2010,99(3-4):357-371

This study aims to trace changes in the dry spells over Peninsular Malaysia based on the daily rainfall data from 36 selected rainfall stations which include four subregions, namely northwest, west, southwest, and east for the periods of 1975 to 2004. Six dry spell indices comprising of the main characteristics of dry spells, the persistency of dry events, and the frequency of the short and long duration of dry spells will be used to identify whether or not these indices have increased or decreased over Peninsular Malaysia during the monsoon seasons. The findings of this study indicate that the northwestern areas of the Peninsular could be considered as the driest area since almost all the indices of dry spells over these areas are higher than in the other regions during the northeast (NE) monsoon. Based on the individual and the field significant trends, the results of the Mann–Kendall test indicate that as the total number of dry days, the maximum duration, the mean, and the persistency of dry days are decreased, the trend of the frequency of long dry spells of at least 4 days is also found to decrease in almost all the stations over the Peninsula; however, an increasing trend is observed in the frequency of short spells in these stations during the NE monsoon season. On the other hand, during the southwest monsoon, a positive trend is observed in the characteristics of dry spells including the persistency of two dry days in many stations over the Peninsula. The frequency of longer dry periods exhibits a decreasing trend in most stations over the western areas during both monsoon seasons for the periods of 1975 to 2004.  相似文献   

The best fitting distribution of annual maximum rainfall in Peninsular Malaysia based on methods of L-moment and LQ-moment     

Wan Zawiah Wan Zin  Abdul Aziz Jemain  Kamarulzaman Ibrahim 《Theoretical and Applied Climatology》2009,96(3-4):345-345

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Runoff Estimation and Morphometric Analysis for Hesaraghatta Watershed Using IRS–1D LISS III FCC Satellite Data     

R. K. Somashekar  P. Ravikumar  S. V. Sowmya  Mubhashir Aziz Dar  A. S. Ravikumar 《Journal of the Indian Society of Remote Sensing》2011,39(1):95-106

The study area, Hesaraghatta watershed is located between 77° 20′ to 77° 42′ E longitude and 13° 10′ to 13° 24′ N latitude with an area of 600.01 km². Thematic layers such as Land Use/Land Cover, drainage, soil and hydrological soil group were generated from IRS–1D LISS III satellite data (FCC). An attempt was made to estimate runoff using Soil Conservation Service (SCS) curve number model and it was estimated to be 1960, 2066, 1870 and 1810 mm for sub-watersheds 1, 2, 3 and 4 respectively. Quantitative morphometric analysis was carried out for the entire watershed and the four sub-watersheds independently by estimating their (a) linear aspects like stream order, stream length, stream length ratio, bifurcation ratio, length of overland flow, drainage pattern (b) aerial aspects like shape factor, circulatory ratio, elongation ratio and drainage density and (c) relief aspects like basin relief, relief ratio, relative relief and ruggedness number. Drainage density was estimated to be 1.23 km/km² designating the study area as a very coarse textured watershed.  相似文献   

The geochronology and petrogenesis of Walash volcanic rocks,Mawat nappes: constraints on the evolution of the northwestern Zagros suture zone,Kurdistan Region,Iraq   总被引：1，自引：0，他引：1  

Khalid J. A. Aswad  Azzam H. M. Al-Samman  Nabaz R. H. Aziz  Alan M. A. Koyi 《Arabian Journal of Geosciences》2014,7(4):1403-1432

Geological, geochemical, and geochronological investigations of the upper volcanics (UV) of Lower allochthon (LA) of Mawat nappes (MN) were used to elucidate the geologic relationships between the LA, the Qulqula Rise (i.e., accretionary complex terrane (ACT)) and peripheral Foreland Basin Assemblage (FBA), (Maastrichtian–Paleogene). The ⁴⁰Ar-³⁹Ar geochronological data suggest that the Middle to Late Paleogene magmatic history of Late Walash arc volcanic activity of UV can be divided into an early phase of andesitic volcanism around 43.1?±?0.3 Ma and subsequent extensional arc phase magmatism of a time lapse between 40.1?±?0.3and 32.3?±?0.4 Ma. The geochemical data establish the existence of gradients in trace element ratios (i.e., Ba/La, Th/Yb, U/La, Ba/Th, Rb/Y, Ba/Y, and Nb/Y) throughout the studied samples and reflect differences in the degree of mantle wedge depletion influenced by addition of a considerable proportion of sedimentary derived input of the subducting Arabian slab. The trace, rare earth elements and isotopes of the studied samples have emphasized differences in the geochemical characteristics of andesites in comparison with other members of Walash. The andesites have subduction-related signature with the isotope (low Nd and high Sr isotope ratios) characteristic of a melt component input from cratonically-derived sediments. The diabases intruding in the basalts and andesites have a transitional composition from andesitic to N-type mid-ocean ridge basalts geochemistry with a noticeable subduction-related signature, and are interpreted to form in an extensional arc evolving into back arc basin setting. As evidenced from infant arc magmatism (Albian–Cenomenian), MN recorded protracted kinematic at convergent plate margins with a most notable was the development of the ACT (i.e., Qulqula Rise) adhered to the Arabian platform carbonates (Albian–Cenomenian) leading to the inception of peripheral FBA occurred by the erosion and unroofing of advancing ACT. Notably, the volcano flysch of Walash and Nummulite carbonate of Naopurdan were still accumulating on the remaining oceanic lithosphere further to the northeast and in part coeval with Paleogene molasses sedimentation on flexural FBA further to the southwest of the ACT.  相似文献   

Mean runoff coefficient estimation for ungauged streams in the Kingdom of Saudi Arabia     

Abdul Aziz Saleh Al-Hasan  Yousry El-Sayed Mattar 《Arabian Journal of Geosciences》2014,7(5):2019-2029

Runoff coefficient estimation in ungauged watersheds has a priority for rain water harvesting and management of runoff water, for domestic and agriculture activities, in semi-arid and arid regions. To estimate mean runoff coefficient (C _Re) for ungauged streams, Pearson's coefficient of linear correlation (r) was measured. The method of linear regression (y?=?mx?+?c) was applied for 16 gauged catchments representing several regions in the Kingdom of Saudi Arabia, such as Al Qassim, Al Madinah, Riyadh, Asir, Makkah, and Jazan. The studied catchments were equally divided into two groups based on their main streams slopes; group A includes eight gauged streams having main stream slope less than 0.01, where group B includes eight gauged streams having main stream slope equal to or greater than 0.01. The result yields the constant of the linear regression for each group and the mean runoff coefficient of basin by an independent value (basin slope) for group A and an independent value (stream slope) for group B. The results indicate that the measured runoff coefficient (C _Rm) and the estimated runoff coefficient (C _Re) are almost equal to each other.  相似文献   

Effects of Cyclic Loading on the Shear Behaviour of Infilled Rock Joints Under Constant Normal Stiffness Conditions     

Ali Mirzaghorbanali  Jan Nemcik  Naj Aziz 《Rock Mechanics and Rock Engineering》2014,47(4):1373-1391

The variation of the shear strength of infilled rock joints under cyclic loading and constant normal stiffness conditions is studied. To simulate the joints, triangular asperities inclined at angles of 9.5° and 18.5° to the shear movement were cast using high-strength gypsum plaster and infilled with clayey sand. These joints were sheared cyclically under constant normal stiffness conditions. It was found that, for a particular normal stiffness, the shear strength is a function of the initial normal stress, initial asperity angle, joint surface friction angle, infill thickness, infill friction angle, loading direction and number of loading cycles. Based on the experimental results, a mathematical model is proposed to evaluate the shear strength of infilled rock joints in cyclic loading conditions. The proposed model takes into consideration different initial asperity angles, initial normal stresses and ratios of infill thickness to asperity height.  相似文献   

Mechanical Effect of Vetiver Grass Root for Stabilization of Natural and Terraced Hill Slope     

Aziz  Shamontee  Islam  Mohammad Shariful 《Geotechnical and Geological Engineering》2022,40(6):3267-3286

Geotechnical and Geological Engineering - This paper studies the role of vetiver grass (Vetiveria zizanoides) on the stability of hill slopes through physical and numerical modeling. Vetiver...  相似文献   

Soil erosion assessment on hillslope of GCE using RUSLE model     

Md. Rabiul Islam  Wan Zurina Wan Jaafar  Lai Sai Hin  Normaniza Osman  Moktar Aziz Mohd Din  Fathiah Mohamed Zuki  Prashant Srivastava  Tanvir Islam  Md. Ibrahim Adham 《Journal of Earth System Science》2018,127(4):50

A new method for obtaining the C factor (i.e., vegetation cover and management factor) of the RUSLE model is proposed. The method focuses on the derivation of the C factor based on the vegetation density to obtain a more reliable erosion prediction. Soil erosion that occurs on the hillslope along the highway is one of the major problems in Malaysia, which is exposed to a relatively high amount of annual rainfall due to the two different monsoon seasons. As vegetation cover is one of the important factors in the RUSLE model, a new method that accounts for a vegetation density is proposed in this study. A hillslope near the Guthrie Corridor Expressway (GCE), Malaysia, is chosen as an experimental site whereby eight square plots with the size of \(8\times 8\) and \(5\times 5\) m are set up. A vegetation density available on these plots is measured by analyzing the taken image followed by linking the C factor with the measured vegetation density using several established formulas. Finally, erosion prediction is computed based on the RUSLE model in the Geographical Information System (GIS) platform. The C factor obtained by the proposed method is compared with that of the soil erosion guideline Malaysia, thereby predicted erosion is determined by both the C values. Result shows that the C value from the proposed method varies from 0.0162 to 0.125, which is lower compared to the C value from the soil erosion guideline, i.e., 0.8. Meanwhile predicted erosion computed from the proposed C value is between 0.410 and \(3.925\, \hbox {t ha}^{-1 }\,\hbox {yr}^{-1}\) compared to 9.367 to \(34.496\, \hbox {t ha}^{-1}\,\hbox {yr}^{-1 }\) range based on the C value of 0.8. It can be concluded that the proposed method of obtaining a reasonable C value is acceptable as the computed predicted erosion is found to be classified as a very low zone, i.e. less than \(10\, \hbox {t ha}^{-1 }\,\hbox {yr}^{-1}\) whereas the predicted erosion based on the guideline has classified the study area as a low zone of erosion, i.e., between 10 and \(50\, \hbox {t ha}^{-1 }\,\hbox {yr}^{-1}\).  相似文献