Assessing heat risk in a sub-saharan African humid city, Lagos, Nigeria, using numerical modelling and open-source geospatial socio-demographic datasets

Abstract

In Sub-Saharan Africa, many cities are facing an increased risk of heat due to climate change and rapid urbanization. This poses a particular threat in areas with limited adaptive capacity. However, there is a lack of comprehensive heat risk assessment in the region, possibly due to the absence of high-resolution weather data. This study aims to address this gap by proposing and demonstrating a methodology for mapping high-risk areas in a tropical humid city, specifically focusing on Lagos, Nigeria. The approach utilises advanced numerical modelling techniques and open-source geospatial data.

The urbanised Weather Research and Forecasting (WRF) model is employed to simulate Humidex-based heat stress during a specific heatwave event in March 2020. Open-source high resolution geospatial datasets were used to assess heat exposure and vulnerability. The urban areas were classified based on the Local Climate Zone (LCZ) scheme. Spatial analysis techniques, including Moran’s I test and Optimized Hot Spot Analysis (OHSA), were used to identify spatial clustering patterns and hot spots of heat risk areas.

Moreover, using Gi* statistics in OHSA, the risk layer was categorised into hot, cold, and non-significant spots at various levels of significance (90 %, 95 %, and 99 %). Mapping the hot spots at the highest confidence level of 99 % identified Critical Heat Risk Zones (CHRZ), covering an area of approximately 423 km². The results showed significant heat risk in highly urbanised LCZs. Further investigation indicated that the largest proportion of high-risk zones corresponded to densely populated and highly urbanised LCZs- LCZ3 (59 %), LCZ 6(21 %), and LCZ 7(17 %). Notably, these areas coincide with two well-known slums in Lagos, emphasizing the need for targeted interventions and planning measures in these areas.

The findings highlight the magnitude and extent of heat risk within the city and emphasize the urgent need for targeted climate change adaptation and mitigation strategies in the identified high-risk zones.