Impacts of droughts on rainfall use efficiency in different climatic zones and land uses in Iran

Abstract

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.