The frequency, duration, and severity of droughts have increased substantially in recent decades, especially in arid and semi-arid regions of the world. Understanding the responses of Rainfall Use Efficiency (RUE) to drought in different ecosystems and climatic zones is not well understood. In this study, spatiotemporal patterns of RUE and Standardized Precipitation Index (SPI) were investigated in four biomes (agriculture, bare land, forest, and range) and eight climatic zones in Iran from 2000 to 2014 using the global MODIS data (MOD17A3) of a 1-km resolution and precipitation data from meteorological stations across the country. A decreasing spatial trend in RUE was observed from west to east and north-west to south-east implying the role of altitude on spatial variation of precipitation. Based on the proposed RUE classification, nearly 60% of Iran’s lands were classified in class “extremely low” and experienced mild droughts during the study period. The increase of drought severity has resulted in an increase in RUE. Temporal variation of national average RUE in all land uses showed a similar trend and the maximum RUE was observed in agricultural lands followed by forest, range, and bare lands. RUE strongly responded to SPI variations across the eight climatic zones and the four biomes. We found significant and negative slopes of linear regression equations for RUE against SPI across all climatic zones, except the arid zone, representing higher accuracy in humid zones than in arid zones. Land uses showed a significant and negative regression, except in agricultural lands.

近几十年来，干旱的频率，持续时间和严重程度已大大增加，特别是在世界干旱和半干旱地区。对不同生态系统和气候区的降雨利用效率（RUE）对干旱的反应了解得还不够清楚。在这项研究中，利用2000年至2014年伊朗的4个生物群落（农业，光秃秃的土地，森林和山脉）和8个气候带，研究了RUE的时空格局和标准降水指数（SPI）。来自全国各地气象站的1公里分辨率和降水数据。从西到东，从西北到东南，RUE的空间趋势呈下降趋势，这表明海拔高度对降水的空间变化具有重要作用。根据拟议的RUE分类，在研究期间，伊朗近60％的土地被归为“极低”等级，并经历了轻度干旱。干旱严重程度的增加导致RUE的增加。在所有土地利用中，全国平均RUE的时间变化都显示出相似的趋势，在农业用地中，其最大RUE最高，其次是森林，山脉和裸地。RUE对八个气候区和四个生物群落的SPI变化有强烈的反应。我们发现除干旱区以外的所有气候区的RUE相对SPI的线性回归方程的显着和负斜率，与潮湿区相比，在潮湿区的精度更高。除农业用地外，土地利用显示出显着的负回归。