Remote sensing approach for examining changes in water use in relation to climate variability and land cover change

Lushozi, Nqobile Quinton (2019-04)

Thesis (MA)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Water use related research in Southern Africa is currently critical; this is not only a result of current and projected impacts of climate change on water resources but the growing tension among different water users has increased the relevance of water use monitoring. The overarching purpose of the study was to quantify the relationship between evapotranspiration (ET), land cover change and climatic variability. This was done at two spatial scales, provincial and sub-catchment scale. The Inkomati-Usuthu and Wider Cape areas were used as case study sites for the sub-catchment scale. The first objective of the study was to define the current water use status of various land cover classes using 2012 annual MOD16 satellite product data. The median ET (mm) and cumulative water use (Mm3 a-1) were estimated for each land cover class per study area. The results indicated that plantation/woodlots, thicket/dense bush and cultivated perennial land cover classes had the highest annual ET estimates. Land cover classes such as grasslands, shrubland fynbos and low shrubland recorded the highest cumulative water use estimates due to the large areas they cover. The second objective was to describe the linkages between ET, land cover change and three climatic drivers: air temperature, vapour pressure deficit (VPD) and rainfall. This was done using a 13 year (2000 – 2012) monthly historical data set of ET and climatic variables per land cover class. Multiple regression analysis and correlation statistics were used to analyse the relationships between these, ET as a dependent variable and climatic drivers as independent variables. The results indicated that air temperature and rainfall were more important drivers of ET changes compared to VPD. In terms of the relationship between ET and the climatic variables, the following was determined: a positive relationship was found between ET and air temperature; a negative relationship was found between ET and rainfall in winter rainfall areas while a positive relationship was reported in summer rainfall areas; no clear relationships were found between ET and VPD. The final objective was to project future changes in water use as a function of climatic and land cover changes by developing a scenario tool for this purpose. Multiple regression equations, means and standard deviations of the climatic variables from the historical analysis were applied in the developed tool. The tool has three main scenarios: land cover change only, climatic change only and a scenario combining the impact of land cover changes and climatic variability on monthly water use per land cover class in each study area. The results from the tool showed that reduction of plantation/woodlots has the greatest impact in decreasing water use. In addition to this the results showed that future increase in air temperature and VPD will result in an increase in water use. This study has been able to describe the relationships between water use, climatic variability and land use. In addition, although the future projections of water use are just estimates, they are useful to initiate dialogues between water users and managers about possible future scenarios.

AFRIKAANSE OPSOMMING: Watergebruikverwante navorsing in Suid Afrika is van kritiese belang. Dit is nie net die gevolg van die huidige en geprojekteerde impak van klimaatsverandering op waterhulpbronne nie, maar die toenemende spanning tussen verskillende watergebruikers het die toepaslikheid van watergebruikmonitering verhoog. Die oorkoepelende doel van hierdie studie was om die verhouding tussen evapotranspirasie (ET), grondbedekkingsverandering en klimaatsveranderlikheid te kwantifiseer. Dit is gedoen op twee ruimtelike skale, provinsiaal sowel as subopvangsgebied. Die Inkomati-Usuthu en Wyer Kaapse gebiede is as gevallestudies vir die subopvangsgebiedskaal gebruik. Die eerste doel van die studie was om die huidige watergebruikstatus van verskillende grondbedekkingsklasse te definieer met behulp van 2012 se jaarlikse MOD16 satellietprodukdata. Die mediaan ET (mm) en kumulatiewe watergebruik (Mm3 a-1) is bereken vir elke grondbedekkingsklas per studiegebied. Die resultate het aangedui dat plantasie-, digte bos- en bewerkte meerjarige landbouklasse die hoogste jaarlikse ET-ramings gehad het. Grondbedekkingsklasse soos grasvelde, fynbos en lae struike het die hoogste kumulatiewe waterverbruiksramings aangeteken as gevolg van die groot areas wat hulle beslaan. Die tweede doel was om die verband tussen ET, grondbedekkingsverandering en drie klimaatsveranderlikes te beskryf: lugtemperatuur, dampdrukstekort (VPD) en reënval. Dit is gedoen met behulp van 'n 13-jarige (2000 - 2012) maandelikse historiese datastel van ET en klimaatsveranderlikes per grondbedekkingsklas. Meervoudige regressie-analise en korrelasiestatistieke is gebruik om die verhoudings tussen ET as afhanklike veranderlike en die onafhanklike klimaatsveranderlikes te analiseer. Die resultate het aangedui dat lugtemperatuur en reënval belangriker bepalers van ET veranderinge was in vergelyking met VPD. In terme van die verwantskap tussen ET en die klimaatveranderlikes, is die volgende bepaal: 'n positiewe verhouding is gevind tussen ET en lugtemperatuur; 'n negatiewe verhouding is gevind tussen ET en reënval in winterreënvalgebiede, terwyl 'n positiewe verhouding in somerreënvalgebiede gerapporteer is; geen duidelike verhoudings is gevind tussen ET en VPD nie. Die finale doel was om toekomstige veranderinge in watergebruik as 'n funksie van klimaats- en landbedekkingsveranderings te voorspel deur 'n scenario-instrument vir hierdie doel te ontwikkel. Die meervoudige regressievergelykings, gemiddeldes en standaardafwykings van die klimaatsveranderlikes uit die historiese analise is toegepas in die ontwikkelde instrument. Die instrument maak voorsiening vir drie scenarios: slegs grondbedekkingsverandering, slegs klimaatsverandering en 'n scenario wat die impak van grondbedekkingsveranderinge en klimaatsverandering op maandelikse watergebruik per grondbedekkingsklas in elke studiegebied kombineer. Die resultate van die instrument het getoon dat die vermindering van plantasies die grootste impak het op dalende watergebruik. Daarbenewens het die resultate getoon dat toekomstige toename in lugtemperatuur en VPD tot 'n toename in watergebruik sal lei. Hierdie studie was in staat om die verwantskappe tussen watergebruik, klimaatsveranderlikheid en grondbedekking te beskryf. Daarbenewens, hoewel die toekomstige projeksies van watergebruik net ramings is, kan dit nuttig gebruik word om dialoog tussen watergebruikers en bestuurders oor moontlike toekomstige scenario's te bewerkstellig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105907
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