Estimation of erosivity and precipitation maps in areas with limited number of rainfall station (Case study: Semnan province)

Document Type : Research Paper

Authors

1 Department of desertification, Faculty of Desert Science, Semnan University, Semnan, Iran.

2 Department of Arid lands management, Faculty of Desert Science; Semnan University. Iran.

3 Department of Arid lands management, Faculty of Desert Science; Semnan University, Semnan, Iran

4 Department of desertification, Faculty of Desert Studies, Semnan University, Semnan, Iran

Abstract

Rainfall erosivity (R) is one of the factors in this model. Direct calculation of R required meteorological gauge stations which are available at a limited number of synoptic stations. In this study, we tried to estimate rainfall erosivity using available data such as annual rainfall. Semnan province, with an area of 96816 km2, has a limited number of synoptic and rain gauge stations, which makes it difficult to estimate rain erosivity in this province. In this study the auxiliary variables including digital elevation model (DEM), normalized vegetation index (NDVI), land surface temperature (LST) and global precipitation network data "Open Land Map Precipitation" (LMP) were used for spatial prediction of annual rainfall. The rainfall map of the study area was prepared using auxiliary data and using random forest (RF) model. Also in synoptic stations, the amount of erosivity based on the EI30 index and average annual rainfall were determined. Finally, the relation between rainfall and erosivity and annual rainfall was determined using nonlinear regression. Root mean square error (RMSE) and coefficient of correlation (r) of RF model for prediction of annual rainfall were 16.9 mm and 0.98, respectively. The results of the rainfall map in study area showed that the rainfall varied between 70-420 mm year-1. Rainfall classification maps showed that near the half of the study area has annual rainfall less than 100 mm, 30% of the province has annual rainfall of between 100 and 150 mm and only about 17% of the province has annual rainfall more than 150 mm year-1. The maximum and minimum values of erosivity were 380 and 39 MJha-1mm h-1year-1 in the northern and southern part of the study area, respectively.

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