西藏青稞灌溉定额的空间分布规律

摘要

西藏地区灌溉定额等试验数据有限，因此，基于少量实测数据，计算分析作物净灌溉定额及其空间变化规律，扩展有限数据的使用范围具有十分重要的意义。基于拉萨站实测的青稞作物系数，采用FAO提出的作物系数修正方法，得到西藏4个农业分区中代表站的青稞作物系数值。基于青稞种植区共28个站点的气象资料及4个分区的青稞作物系数及土壤水分参数等资料，采用土壤水量平衡原理计算得到28个站的青稞灌溉定额长系列值。采用克里金插值法得到西藏青稞不同水文年型灌溉定额及其主要影响因子的等值线图，分析了青稞灌溉定额的空间变化规律及其与主要影响因子的关系。结果表明，从西北到东南，青稞灌溉定额呈现逐渐减小的变化趋势，其等值线总体呈带状分布特点，并且等值线与经线趋于平行。青稞灌溉定额随着降雨量增加而降低，随气温及ET0增加而增加。%The objective of this study was to estimate the irrigation water quota and their spatial distribution of highland Barley in Tibet. Tibetan plateau has the characters of high altitude, low air pressure, vast geographic, and has significant differences on climate spatial distribution. Until now, Tibet has very few measured irrigation and drainage experiment data of crops. This paper tried to combine theoretical calculation and survey data together to find a method to calculate the irrigation water quota and obtain a contour map under different irrigation frequency in convenient for project design. Four represent highland barley planting sites in each of four agricultural growth partitions of Tibet were selected to get information on irrigation, cultivation, soil conditions and meteorological characteristics, then 28 meteorological stations’long series of climate data were gathered. To calculate the accurate irrigation water quota of Tibet highland barley, water balance method was applied to calculate daily water balance processes during the growth period. In this process, precipitation, effective precipitation, root zone soil moisture, evapotranspiration, percolation, drainage and so on factors were used. Root zone’s soil water was determined by scheming wetness depth and appropriate upper and lower soil moisture limit, and ETc(evapotranspiration) was determined by FAO. Kcini, Kcmid, Kcend were modified considering soil and crop evaporation separately by recommended dual crop coefficient. Kc of four typical sites were calculated, and then irrigation water quota from 1957 to 2009 were calculated by daily water balance in different hydrological years. By comparing the calculated results with surveyed irrigation data, four sites’calculated results were validated, and then the other 24 sites of the 4 partitions’irrigation water quota were also calculated. According to 28 sites’results, Kringing interpolation method was used to get the contour map of Tibet highland barley irrigation water quota in different hydrological years. Climate factors that may interpret irrigation water quota for highland barley were analyzed using Kringing method and contour maps were also obtained. Results showed, in general, from the northwest to the southeast, irrigation water quota decreased gradually. Highland barley irrigation water quotas in Tibetan decreased with precipitation and increased with temperature and ET0.