Spatially explicit predictions of changes in the extent of mangroves of Iran at the end of the 21st century

This is the first study that uses a spatially explicit approach to predict the remaining area of mangroves accounting for predicted changes in rainfall and sea levels caused by climate change. Rainfall/drought intensity and sea level rise were predicted for the end of the 21st century using the RCP8.5 climate change scenario for three study sites that were located on the semi-desert coasts of the Persian Gulf (PG) and the Gulf of Oman (GO) of Iran. Satellite images revealed that the spatial dynamics of mangroves diverged over the last 32 years. During the most recent wet period (1986–1997), mangroves expanded and increased their net areas despite rising sea levels of about 3.3 mm yr⁻¹. During the most recent dry period (1998–2017), mangroves gradually retreated from landward positions and lost area following seaward inundation by rising sea waters; more abundant short-term rainfall did not lead to expanding mangrove areas. The Cellular Automaton (CA)-Markov algorithm and statistical modeling were used to model mangrove areas during the wet and dry periods, accounting indirectly (CA-Markov) or directly (statistical) for rising sea levels and precipitation/droughts. Mangrove areas in the year 2100 predicted with the CA-Markov algorithm were spatially-explicitly adjusted for expected sea levels in a GIS. The statistical model developed for the most recent dry period, most similar to the anticipated future climate, was parameterized with the expected rainfall data and sea levels in 2100. Both CA-Markov and statistical modeling predicted that regional mangrove area will decline between 50 and 60%, with the greatest decline on the coast of the GO where sea level rise is exacerbated by greater subsidence rates than sedimentation rates. Compared to 2017, increased rainfall and decreasing drought severity forecast in 2100 in an overall dry period are not sufficient to reverse the reductions in mangrove areas following rising sea levels of ~9.9 mm yr⁻¹ expected between 2017 and 2100.