Sensitivity Of The Potential Evapotranspiration To Different Climatic Regions From1960to2009in Gansu Province

Potential evapotranspiration,as an estimate of the evaporative demand of theatmosphere,has been widely used in researching on irrigation management, corp waterdemand and predictions in ungauged basins.Gansu province belongs to fragileecological environment area and is sensitive to climate change.Study of potentialevapotranspirati-on change law,influence factors and response mechanism are worthpaying attention.In the paper,seven climate regions were divided from27weather stationsaccording to the standard of Li Dongliang in Gansu province.Based on themeteorological data from1960to2009,the FAO recommended correction thePenman-Monteith formula, liner trend and ArcGIS （Inverse Distance Weighted） wereused to analyse the space distribution features of the ETO,ETearo and ET_rad.We try tocombine the two methods of sensitive coefficient and contribution to analyse thereason of ETO.The results of the study were shown as follows:1.In recent50years, ETOincreased except the warm-temperate,warm-temperate,cold-temperate arid climatic region of Hexi. The ETOvaries in different climateregions in Gansu, with the peak in summer and the bottom in winter, while the ones inautumn and spring were in the middle. Different climate region has different inter-decadal change. Firstly, the ETOincreased and then decreased in the semi-aridclimatic region in the northern of Longzhong. But the pattern in other climate wasincrease-decrease-increase. The ETOhad the characteristics of remarkable spatialvariation, such as decreasing from northwest to southeast,which showed the ETOwasthe smallest in Gannan plateau （Hezuo）,while the ETOwas the biggest in western ofHexi plain （Gouzhou）.The amount of ETearoand ET_radwere equal in the arid climateregion of warm-temperate and cold-temperate of Hexi,but in other climatic regionswere ET_rad> ET_earo.In the seven climate regions, the ET_radwas rising. The warmtemperate arid climate region increased obviously.The trend of ETearowere decreasingin the warm-temperate, cold-temperate arid climatic region of Hexi,high-coldsemi-arid and semi-humid region of Qilian mountains, and the semi-arid climateregion in the northern of Longzhong,whlie the other three climate region increased.2. The recent50years, the sensitive coefficient of R_nhad the highest amount indifferent climate of Gansu province.The pattern of sensitive coefficient of ETOwas R_n>RH>T_max>U₂>T_minin the humid climatic region of Longnan, high-cold humidclimatic region of Gannan, the semi-arid region in the northern Longzhong and thesemi-humid region in the southern Longzhong. High cold semi-arid and semi-humidclimatic region of Qilian mountains were R_n>RH>U₂>T_max>T_min,While thewarm-tem-perate, cold-temperate arid climatic region of Hexi were R_n>T_max>U₂>RH>T_min.The sensitive coefficient of RH was negative, whereas the value of R_n, U₂andT_maxwas positive. T_minwas negative in the high-cold humid climatic region ofGannan,the high-cold semi-arid and semi-humid climatic regions of Qilian Mountains,cold-temperate arid climatic region of Hexi.3. In different climate zone, the contribution to ETOvaries indifferent weatherfactor. RH was the highest contribution, followed by U₂in humid climatic region ofLongnan. In the warm-temperate, cold-temperate arid region of Hexi, U₂and T_maxofcontribution amount significantly, especially in the warm-temperate arid region ofHexi, partically the wind speed of contribution up to12.795%. In all the other fourclimate regions,the highest contributions climate factor were consistent, were T_max. Inthe arid areas of ETO. The most significant contribution was U₂. In semi-arid andsemi-humid climatic region and high altitude area, the most significant contributionwas T_max.In the humid climatic region, the contribution rate of RH was the biggest.4. Combining the two methods of sensitive coefficient and contribution toanalyse the reason of ETO.R_n and U₂was the important climatic factor to the ETOinthe warm-temperate and cold-temperate arid climatic region of Hexi. R_nand T_maxwas the main climatic factor to impact ETOin the northern Longzhong and thesemi-humid climatic region in the southern Longzhong, high-cold humid region ofGannan, high-cold semi-arid and semi-humid climatic regions of Qilian mountains.R_n was the most significant climate factor, followed by the RH and U₂In humidclimatic region of Longnan.