Analysis of drought patterns in the Tano river basin of Ghana

Abstract

The objective of this study is to analyze drought patterns in the Tano River Basin (TRB) of Ghana using Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI). Precipitation data from 1981 to 2019 for the TRB was accessed from Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), extracted into time Series using Python to four locations within the basin and used for the analysis together with the National Aeronautics and Space Administration (NASA) POWER (Prediction Of Worldwide Energy Resource) Temperature data. Anderson-Darling test was performed to check for the normality of the precipitation. Two separate station data sets from TAHMO and Earth Observation Research Innovation Centre (EORIC) were used to validate the CHIRPS data. The Scaler Index (SI) from the two data sets are respectively 0.383 and 0.016. This indicates the CHIRPS data extracted is sufficiently accurate. The SPI and RDI on the time scales of 1, 3, 6 and 12 months were calculated using the Drought Indices Calculator (DrinC) software and characterized into the magnitude, duration, and severity of the drought. Regression analysis was performed to compare RDI and SPI values. The results show that the coefficient of regression R2 is 0.9789, 0.9689 and 0.8799 for 1, 6 and 12 months respectively. This indicates a stronger correlation between SPI and RDI values. However, R2 is observed to decreases with increasing time scale, which means for shorter time scales, SPI and RDI are more similar than for longer time scales. To further examine the possible impacts of climate change on the drought profile of the basin, the Mann-Kendall trend test was conducted to compare the trends in SPI and RDI for 1, 6 and 12 timescales. Apart from RDI 6 for Tanoso which recorded a decrease in trend of – 0.17 as against 0.14 of SPI 6, all other timescales recorded an increase in trend for RDI as compared to SPI. Although most of these increases in trend is not significant at 10% significance level, a trend of 1.95 and 1.71 of RDI 1 for Buako and Sepremboi respectively were significant compared to that of SPI 1 for same stations. These increases in trend of RDI as compared to SPI suggests the possible impact of climate change since RDI estimation takes into consideration potential evapotranspiration (PET), which is a factor of temperature. This could have negative implications on agricultural production and drinking water supply within the basin considering that the basin solely relies on surface water for crop production and drinking water supply.