Climatic change of terrestrial surface humid index and its impact factors over the source region of three rivers in recent 50 years

Based on climatic observational data of monthly average temperature,maximum temperature,minimum temperature,relative humidity,precipitation,wind speed and sunshine duration over the source region of three rivers in the year 1959—2008,the data of maximum potential evapotranspiration(ET0) and terrestrial surface humid index was computed by revised Penman-Monteith Model.The distribution,inter-annual change and the seasonal difference of ET0 and surface humid index were analyzed,and the climatic impact factors for the change trend of surface humid index were discussed.The main results were as follows: In 1959—2008,the annual precipitation in this region had an increased trend,the annual precipitation change curves’ linear fitting rate is 5.316-13.047 mm.(10a)-1,and the increasing rate mostly appeared bigger in spring and summer.The annual ET0 displayed an ascending trend as well,and the linear fitting rate of the annual ET0 change curves is 5.073-10.712 mm.(10a)-1,the biggest increasing rate appeared mostly in summer.The surface humid index displayed an ascending trend,with the linear fitting rate of its change curves being 0.011-0.026(10a)-1,the biggest increasing rate appeared mostly in winter.The climatic 3-5 periods of dry and wet alternation happened about every 15 a period of time and frequency,which was the light wet stages since 1984,while the light dry stages appeared at a higher frequency in 1998—2006.The main factors which could influence the surface humid index were the precipitation,the relative humidity and the average maximum temperature.