Land Use Change, Modelling of Soil Salinity and Households’ Decisions Under Climate Change Scenarios in the Coastal Agricultural Area of Senegal

Abstract

Soil salinity remains one of the most severe environmental problems in the coastal agricultural areas in Senegal. It reduces crop yields thereby endangering smallholder farmers’ livelihood. To support effective land management, especially in coastal areas where impacts of climate change have induced soil salinity and food insecurity, this study investigated the patterns and impacts of soil salinity in a coastal agricultural landscape by developing an Agent-Based Model (ABM) for Djilor District, Fatick Region, Senegal. Landsat images for 1984, 1994, 2007 and 2017 combined with normalised difference vegetation index (NDVI), elevation, wetness index and distance to the river were used to determine Land use-land cover and salinity changes. Land use classification and intensity analysis were applied to determine the time intervals during which the annual change area is relatively slow versus fast, and the variation of the categories’ gains and losses during a time interval. Soil samples plots (at 0-30 cm depth) were collected according to different land use, soil and crop types to determine the salinity patterns. Households’ survey data were collected based on 304 selected respondents to assess the perception and adaptation strategies of farmers. Land Use-Salinity Interaction (LUSI) was developed to explore the potential impacts of increased temperature and farmers’ decisions on soil salinity dynamics. Salt content, crop yield and households’ decisions sub models were incorporated in LUSI model. Three scenarios were simulated over a 20-year period, namely Baseline (current trend), 1 °C increase in temperature (Temp1) and 2 °C increase in temperature (Temp2). Eight LULC were identified in Djilor: mangrove, forests, savannah shrubs, croplands, bare lands, salt marshes, sabkha and water bodies. Forests and croplands constitute the major land use in terms of area. Croplands recorded the highest gain (17 %) throughout the period from 1984 and 2017, while forest registered the highest loss (12.5 %). The time interval 1984-1994 had the fastest annual area change. Regarding soil salinity, bare lands, fallow lands, rice plots and Fluvisols registered high values in salt content. Clay content, elevation and distance to river were the important factors associated with the increased salt content. In 1984, highly saline and moderately saline areas were the largest in extent 32.65 % and 38.9 %, respectively. In 2017, slightly saline areas increased to 39.69 %, while highly saline and moderately saline areas decreased to 20.85 % and 25.60 %, respectively. Sabkha and salt marshes cover had the largest salt-affected areas over time. Regarding the social response to salt content, local perception of soil salinity indicates a general increase of soil salinity in the area. Women group engaged in rice farming appeared to be more affected by soil salinity. To cope with the negative impact of soil salinity, the farmers’ strategies are mainly the application of chemical fertilizer and manure, planting and conservation of trees, and installation of soil bunds. Simulation of soil salinity under current conditions showed an increasing trend of salinity over the next 20 years. The average EC was 6.48 dS/m and 9.77 dS/m for Temp1 and Temp2 scenarios, respectively for the period 2017-2036. Temp1 and Temp2 scenarios will contribute to increase the mean EC by 7.7 % and 15.8 % per year, respectively. Simulated salinity will also contribute to decrease crop yield. Rice crop registered the lowest yield over time with 228, 187, 149 kg ha-1 y-1 in BAS, Temp1 and Temp2, respectively, compared to maize, millet and groundnut. This study recommends the implementation of appropriate land management and mitigation strategies for preventing climate change and its effects on salinity dynamics in the coastal regions of Senegal by policy makers and other stakeholders.