Modelling historic and future land use/land cover changes and their impact on wetland area in Shashe sub-catchment, Zimbabwe

Abstract

The purpose of this study was to use current and historic land use/land cover (LULC) changes to predict future LULC using coupled Cellular Automata–Markov chain model. Landsat time series data for the month of June were used to determine LULC changes for the years 1984, 1995, 2005 and 2015 using random forest classification system in R. We then used Markov Chain algorithm with multiple perceptron in land change modeler to simulate future LULC dynamics for the years 2025, 2035 and 2045. Contingent valuation method was employed to estimate ecological value of wetlands. Results for the LULC analysis for the period between 1984 and 2015 show a decline in woodland and wetland area owing to natural and human factors. We noted a reduced net change for grassland, woodland and mountain vegetation covers losing by − 4%, − 5.2%, − 2% and − 4% change, respectively. While, riverine vegetation, crop field and rock outcrop gained by 0.5%, 4% and 10.2%, respectively. A notable dramatic decline in wetland area was recorded between 1995 and 2005 losing about 125.53 ha, which could be attributed to recurrent droughts of 1995, 1998, 2002 and 2005. Major conversions were from wetland cover to crop fields suggesting agricultural encroachment onto the wetland area. Wetland area, thus, significantly decreased by 6% (p < 0.05) amounting to 236.52 ha in the last 30 years. Coupled CA–Markov chain model results for the years 2025, 2035 and 2045 predicted a further increase in cropfield at the expense of woodland and wetland area. In particular, wetland area is expected to further shrink by 46% (72.67) by the year 2045. Contingent valuation results show that every respondent concurs that wetlands have deteriorated to a very bad state in comparison to their state in the twentieth century. The cited reduced wetland health, biodiversity of both flora and fauna, water quality and quantity and general wetland area. The present state is estimated to be far less than 10% of the total value of wetlands 20 years ago. Quantifying such future wetland area changes is important not only for pure-scientific purposes but also for appropriately developing locally relevant and sustainable management strategies for wetland conservation.