Assessing land use/land cover change impacts on the hydrology of Nyong River Basin, Cameroon

Abstract

Uncontrolled land use land cover change (LULCC) is impacting watershed hydrology, particularly in tropical watersheds in developing countries. We assessed the extent of LULCC in the southern portion of the Nyong River basin through analysis of three land use maps in 1987, 2000 and 2014. LULCC impact on hydrological variables of the Mbalmayo, Olama, Pont So’o, Messam, and Nsimi sub-watersheds of the southern portion of the Nyong River basin were evaluated by using the linear regression modeling and the Mann-Kendall test. This study reveals that dense forest cover decreased by 16%, young secondary forest increased by 18%, agricultural/cropland increased by 10%, and built-up area/bare soil increased by 3% from 1987 to 2014. The decrease in dense forest cover at 0.6% per year on average was driven by indiscriminate expansion of subsistence agricultural/cropland through shifting and fallow cultivation farming systems. Nonsignificant trends in total discharge, high flows, and low flows were observed in the large sub-watersheds of Mbalmayo and Olama from 1998 to 2013 with LULCC within the watershed. In contrast, significant decreasing trends in stream discharge (up to −5.1% and −5.9%), and significant increasing trends in high flows (up to 2.1% and 6.3%), respectively, were observed in the small sub-watersheds of Pont So’o and Messam from 1998 to 2013, particularly with increase in agricultural/cropland cover and decrease in dense forest cover. However, we found non-significant trends in mean annual discharge and low flows for all and whole watershed with LULCC. The results reveal spatially varying trends of stream discharge, low flows and high flows among the sub-watersheds with LULCC within the study watershed. The results suggest that the impacts of LULCC on watershed hydrology are easily detected in small sub-watersheds than in large sub-watersheds. Therefore, the magnitude of dense forest cover loss must be significantly greater than 16% to cause significant changes and common trends in the hydrology of the sub-watersheds of the southern portion of the Nyong River basin. The Mann-Kendall and Regression approaches show appreciable potential for modelling the impacts of LULCC on the hydrology of the southern portion of the Nyong River basin and for informing forest management.