School of Geography, Archaeology and Environmental Studies An assessment of the impacts of climate and land use/cover changes on wetland extent within Mzingwane catchment, Zimbabwe. BY SETHI SIBANDA (1019068) Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Geography and Environmental Science) Supervisors: Prof. Fethi Ahmed Prof. Stefan Grab June 2018 i DECLARATION I declare that this work is my own original work and has not been previously submitted to obtain any academic qualification. Data and information obtained from published and unpublished work of others have been acknowledged in the text and a list of references is herein provided. Signature: ------------------------------------ Date: ----------------------------------------- i DEDICATION To my late father with love ii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my supervisors, Prof. Fethi Ahmed and Prof. Stefan Grab for their exceptional academic guidance, encouragement, and support throughout the study. Truly, the experience was academically rewarding. I also appreciate the financial support I received from Prof. Fethi Ahmed, without such support this study was not going to be possible. I also acknowledge various institutions that provided data for the study. I am greatly indebted to my husband and family who have been a pillar of strength throughout the study. Lastly, I would like to extend my gratitude to all my friends and colleagues from Lupane State University whose moral and academic support contributed to the success of this study. iii ABSTRACT Wetlands ecosystems are amongst the most diverse and valuable environments which provide a number of goods and services pertinent to human and natural systems functioning yet they are increasingly threatened by anthropogenic and climatic changes. This thesis, examines the impact of climatic trends and variations, and land use/land (LU/LC) cover changes on wetland extent within Mzingwane catchment, south-western of Zimbabwe. An attempt is made to establish how the two stressors (climate and LU/LC changes) modify areal extents of wetlands over time, grounded on the hypothesis that, climate and LU/LC related changes impact on wetland ecosystems resulting in their degradation, shrinking in size and in some cases overall loss. To achieve the broader objective of the study, a number of parametric and non-parametric statistical analyses were employed to quantify and ascertain climate variability and change in Mzingwane catchment through the use of historic and current climatic trends in rainfall and temperature (T). Remote sensing data was used for wetland change analysis for the period between 1984 and 2015as well as future land cover predictions based on CA-Markov Chain model. LU/LC changes on nested wetlands were modelled at catchment level. In addition the study simulated future rainfall and extreme events and their implications on wetland dynamics using Regional Climate Models derived from CORDEX data. -1 Trends in annual Tmax significantly increased (p<0.05) at an average of 0.16 decade in 80% of the stations. Results of extreme events indicate a statistically significant increase (p<0.05) in the occurrence of extreme dry periods since the 1980s. Rainfall variability results show that contemporary mean annual rainfall has not changed from that measured during the historic period of 1886-1906. However, the number of rainy days (>=1mm) has decreased by iv 34%, thus suggesting much more concentrated and increased rainfall intensity. A notable shift in both the onset and cessation dates of the rainy season is recorded, particularly during the 21st century, which has resulted in a significant reduction (p<0.05) in the length of the rainy season. Land change analysis results show a decline in woodland and wetland cover which could be resulting from both human and natural factors. Major conversions are from wetland cover to crop field, suggesting agricultural encroachment onto wetland areas. Wetland area thus significantly decreased by 60.16% (236, 52 ha) in the last 30 years (p < 0.05). CA-Markov model results for the years 2025, 2035 and 2045 predicted an overall increase in the crop field areas at the expense of woodland and wetland areas. LU/LC modelling results suggest that LU/LC changes modify wetland hydrology which consequently influences wetland areal extent. Trend results for projected rainfall suggest a significant decreasing trend in future rainfall (2016-2100) at p<0.05. In addition, a general decreasing trend in the number of rainy days is projected for the future climate although the significance and magnitude varied with station location. Regional Climate Models projections suggest an increased occurrence of future extreme events particularly towards the end of this century. The findings are important for developing appropriate sustainable and adaptive strategies given climate changes as well as designing catchment level wetland management approaches aimed at sustaining wetland ecosystems for the current and future generations. Any future efforts towards protection of the remaining wetlands should be combined with developing a sustainable relationship between social and ecological systems which will enable communities to adapt to the effects of changing climates v TABLE OF CONTENTS DECLARATION ........................................................................................................................ i DEDICATION ........................................................................................................................... ii ACKNOWLEDGEMENTS ..................................................................................................... iii ABSTRACT .............................................................................................................................. iv TABLE OF CONTENTS .......................................................................................................... vi LIST OF FIGURES .................................................................................................................. xi LIST OF ABBREVIATIONS AND ACRONYMS ............................................................... xvi CHAPTER 1: GENERAL INTRODUCTION .......................................................................... 1 1.1 Introduction ...................................................................................................................... 1 1.2 Background to the study ................................................................................................... 3 1.3 Problem statement ............................................................................................................ 5 1.4 Significance of the study .................................................................................................. 5 1.5 Main Aim ......................................................................................................................... 7 1.6 Methodological approach ................................................................................................. 8 1.7 Structure of the thesis ....................................................................................................... 8 CHAPTER 2: GENERAL LITERATURE REVIEW ............................................................ 10 2.1 Introduction .................................................................................................................... 10 2.2 Wetland Ecosystems and their sensitivity to environmental changes ............................ 10 2.2.1 General importance of wetlands .............................................................................. 10 2.2.2 Wetland classification .............................................................................................. 11 2.2.3 Methods of assessing and monitoring wetlands ...................................................... 12 2.2.4 Anthropogenic drivers of wetland loss and degradation ......................................... 15 2.3 Climate Change in Africa ............................................................................................... 17 2.4 Climate change and variability in Zimbabwe ................................................................ 19 CHAPTER 3: SPATIO-TEMPORAL TEMPERATURE TRENDS AND EXTREME HYDRO-CLIMATIC EVENTS IN SOUTHERN ZIMBABWE ............................................ 23 vi 3.1 Introduction .................................................................................................................... 24 3.2 Materials and Methods ................................................................................................... 26 3.2.1 Study region ............................................................................................................. 26 3.1.2 Data acquisition and processing .............................................................................. 28 3.1.3 Spatial distribution of temperature anomalies ......................................................... 29 3.1.4 Trend analysis .......................................................................................................... 30 3.1.5 Seasonal trends in temperature and extreme wet and dry events ............................ 30 3.1.6 Magnitude of trends in temperature and extreme wet and dry events ..................... 31 3.1.7 Standard Precipitation and Evapotranspiration Index (SPEI) ................................