Assessing the skills of inter-sectoral impact model intercomparison project climate models for precipitation simulation in the Gongola Basin of Nigeria

Abstract

Abstract The study quantitatively assesses the ability of five Global Circulation Models (GCMs) in the fast track of Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) to reproduce the observed precipitation climatology over the Gongola river basin of Nigeria for the period 1982−2004. The models present-day precipitation is evaluated relative to Global Precipitation Climatology Centre (GPCC) observational datasets based on spatial analysis, statistical measures and climate indices at annual, monthly and daily cycles. The results show that climate models replicate the annual precipitation pattern well, both spatially and in magnitude with varying margins. Moreover, the GCMs captured the orographic pattern in the Jos plateau and the general decreasing precipitation trend towards the basin s northeast. Among the GCMs, IPSL-CM5A-LR better captured the rainy season in the basin extents from April to October and May to October, respectively, over the Jos plateau and other regions, with maximum rainfall occurring in August, exhibiting a unimodal pattern. The HADGEM2-ES better represented the most occurring rainfall intensity in the basin (5 to 50 mm hr-1) in most regions. The degree of pattern correspondence is found highest for IPSL-CM5A-LR with a correlation coefficient of 0.73. Only HADGEM2-ES was able to capture the spatial variability of maximum consecutive dry days over the study domain, increasing from 150 days around the Jos plateau to 200 days over Uba plain. Findings also reveal that the highest daily rainfall event s intensity is poorly represented by the models, including their ensemble mean. However, HADGEM2-ES exhibited better performance and turnout to be the only model with good skill in replicating this extreme condition. Indeed, no single model systematically performs anomalous, and no individual model performs best at all times over the study domain. Nonetheless, the most skilful models over the Gongola basin are identified for climate impact assessment.