Climate change impacts on hydropower generation in Malawi: a case study of Lujeri micro hydropower scheme in Mulanje district

Abstract

The production of hydroelectric power depends, among others, on discharge which is in turn affected by seasonal and quantitative changes in precipitation and evaporation. Climate change has caused changes in the weather patterns over Malawi, extreme episodes of rainfall and temperatures and has affected hydropower generation by reducing flows (discharge). This is the case with Lujeri hydropower – the subject. The study involved collection of hydrological (river discharge) and weather time series (air temperature and rainfall) data. The data was logically interpreted using Statistical Package for Social Science (SPSS), XLSTAT and Microsoft Excel. Ordinary least squares (OLS) regression analysis was used to determine marginal changes in the climatological time series data. Mann-Kendall (MK) test was used to detect trends in air temperature, precipitation and discharge. Correlation analysis was also used to uncover the relationship between discharge and precipitation as well as between discharge and temperature. The results showed that distribution of annual rainfall in Mulanje area (for period 1959 to 2011) has decreased at the rate of about 2.97 mm per year. The MK test gave a mix of positive and negative trends for the monthly precipitation. Only the month of January showed a positive significant trend while February, March, April, May, June September, and November had a significant negative trend. All three seasons showed decreasing trend in precipitation and the negative trend was statistically significant for cool and wet season. Similarly, temperature analysis revealed a rising trend of about 0.04 °C every year which led to high evaporation. The MK test for temperature results showed a significant increasing trend for both mean monthly and mean maximum temperature. This resulted in decrease in the Ruo River’s, location of Lujeri micro-hydropower, annual mean discharge. Analysis on MK test revealed that there was a positive trend in discharge in the months of January, February, March, April and December. The increase in trend was significant for February, March and April. The results also indicated a statistically significant negative trend in discharge for the rest of the months of the year apart from May. Furthermore, there was a small positive correlation between rainfall and discharge (r = 0.09) although the increase in discharge due to rainfall was not significant (p = 0.55). On the other hand, the relationship between temperature and discharge showed a large, negative correlation (r = - 0.64) and the relationship was significant (p = 0.0001). This means that continued increase in temperature will result in a decrease in discharge. As power generated is proportion to discharge, variation in the river discharge will have direct impact on hydropower vii generation. Therefore, proper adaptation measures were explored to ensure electric power is available throughout the year especially in the hot and dry season, when the discharge is very low.