Spatial-temporal Changes In Evapotranspiration Based On Planting Petterns Of Major Crops In Xinjiang Oasis During 1960~2010

Evapotranspiration(ET)is the most important process of hydrological cycle in the oasis croplands,and is also the major way of water consumption in oasis.The ET based on planting patterns has significant influence on the optimal allocation and reasonable utilization of agricultural water resources in the arid oasis of northwest China.It is also beneficial to the sustainable development of desert ecological environment with oasis as the center.At present,the soil salinization in the inland river basin in the arid region is mainly concentrated in the irrigated farmland,but the level of soil salinization in the oasis and the surrounding desert(hereinafter referred to as oasis)is not clear.From 1960 to 2010,with the excess land reclamation particularly in the rural and moutainous areas,the cultivated land areas of Xinjiang Oasis continued to increase,the spatial datasets of planting pattern including wheat,maize and cotton in Xinjiang were built by integrating agricultural statistics at county-level and cropland area maps extracting from LULC product.Thereafter,the actual ET of croplands and its composition was estimated by FAO Penman-Monteith(P-M)equation and total ET(TET)of each watersheds was calculated through GIS technique.The areas and planting pattern changes of cultivated land have important influence on the temporal and spatial distribution of crop evapotranspiration and the structural change.The results showed that:? With the continued increase of cultivated land area in Xinjiang Oasis in recent 50 years,the total proportion of the three crops was increased from 70.3% to 72.9%,and the general growth rate in the southern watersheds of Xinjiang(12.8%/yr)was higher than that in the norther(1.4%/yr).The planting proportion of cotton and wheat were significantly increased and decreased(39.7 and-15.5%/yr respectively)while maize planting ratio remained stable(-2.8%/yr).?The TET of three crops generally increased from 240.6×108m3 to 539.5×108m3 in Xinjiang during 1960~2010.The contribution rate of cotton,wheat and maize to TET were respectively 61.0%,5.1% and 9.8%.The TET of the northern region of Xinjiang(285.5×108m3)was greater than that in southern region(254.0×108m3)in 2010.The average increase rate of TET in the southern watersheds of Xinjiang was larger than that in the norther.The Manas River watershed in northern Xinjiang has the largest increased ratio of cotton TET and the decreased ratio of wheat TET.The spatial pattern changes of TET was similar to that of planting structure for major crops in Xinjiang agricultural oasis.It implied that the spatial-temporal patterns of croplands would changed that of ET and TET in arid regions.