Drought Assessment by Evapotranspiration in Twente, the Netherlands
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DROUGHT ASSESSMENT BY EVAPOTRANSPIRATION MAPPING IN TWENTE, THE NETHERLANDS UGYEN EDEN February 2012 SUPERVISORS: Dr. Ir. Joris Timmermans Dr. Ir. Rogier van der Velde DROUGHT ASSESSMENT BY EVAPOTRANSPIRATION MAPPING IN TWENTE, THE NETHERLANDS UGYEN EDEN Enschede, The Netherlands, February, 2012 Thesis submitted to the Faculty of Geo-Information Science and Earth Observation of the University of Twente in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation. Specialization: Water Resource and Environmental Management SUPERVISORS: Dr. Ir. Joris Timmermans Dr. Ir. Rogier van der Velde THESIS ASSESSMENT BOARD: Chairman: Prof. Dr. Ir. Z. Su External Examiner: Dr. S. Monincx DISCLAIMER This document describes work undertaken as part of a programme of study at the Faculty of Geo-Information Science and Earth Observation of the University of Twente. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the Faculty. ABSTRACT Drought is a reoccurring worldwide problem with impacts ranging from food production to infrastructure. Droughts are different from other natural hazards (floods, hurricanes, and earthquakes) because the effects are only witnessed slowly and with a time delay. Droughts are caused by natural causes but also by interaction between the natural processes like precipitation and evapotranspiration and water demand. Heat waves and prolonged absence of precipitation is expected to increase due to climate change. Therefore drought is expected to become more frequent in both typical dry regions, like the Horn of Africa, and also in semi-humid environments, like Europe. This gives rise to socio-economic related problems in countries unfamiliar to droughts. Dutch temperature rise and precipitation deficit in the summers of 2003 and 2006 caused substantial crop loss in the agricultural sector. Side effects included increased river water temperatures and low water levels which lead cooling problems for power plants. Therefore assessing and monitoring drought in the Netherlands is thus very important. Drought monitoring is usually performed with drought indices. Various drought indices are available to assess the severity, duration and spatial extend of the drought. Some of the commonly indices used are Standardized precipitation index (SPI) and the Palmer Drought Severity Index (PDSI). However each of these indices do not take into account the actual state of the land surface in respect to the dryness. By analysing drought through actual evapotranspiration (ET) estimations from remote sensing this shortcoming can be avoided. The severity of the droughts was quantified by ET-mapping from 2003-2010. The assessment was based on the spatial and temporal distribution of ET using the Evapotranspiration Deficit Index (ETDI) drought index. Surface energy fluxes, like ET, were estimated using WACMOS methodology. The input data consisted of remote sensing products like land surface temperature, LAI, and albedo from MODIS; and meteorological data like air-temperature, humidity and wind speed from the European Centre for Medium weather forecast (ECMWF). ETDI was then calculated using the estimated actual ET in combination with reference ET from Penman-Moneith. Investigations on temperature and precipitation anomalies, using SPI, are also included because of their contribution to the droughts. For this precipitation data from ground measurements were used to calculate the SPI for comparison with ETDI. The results show that SEBS ET from MODIS 1km resolution and ECMWF can be used for estimating ET for Twente region. The ET maps show that evapotranspiration in all years follow a seasonal trend with higher ET during the growing season as compared to other seasons. Investigation into ET shows small spatial variability, and investigation into SPI shows large temporal variability with 2003, 2006, and 2009 being dry years. The results from ETDI and SPI can be used for drought assessment. Keywords : Drought, ET, SEBS, MODIS, SPI, ETDI. i ACKNOWLEDGEMENTS I would like to express my gratitude to the Netherlands Government for granting me this opportunity to pursue master of science degree. I am grateful to my employer, Ministry of Works and Human Settlement for encouraging me to take up this study. I would like to thank my first supervisor, Dr. Ir. Joris Timmermans for his excellent guidance and encouragement throughout the research period. His continual support and supervision have helped me a lot from the day of commencement of the research work till the completion. I am truly indebted for his support and help during the fieldwork despite the weather conditions. He was always there to help me with programming language used for my research without which the research would not have been possible. I am also thankful to my second supervisor, Dr. Ir. Rogier van der Velde for his valuable comments and advices to improve my research. I would like to thank the farmer of De_Broeze horse and milk farm in Markelo, Goor for letting us use his precious farm land for our station set. To Mr.Murat Ucer for helping me during the field work. To Ms Laura Dente for providing me with the soil moisture data. I thank the Water Board of Regge and Dinkel for providing me with the precipitation data for the research work. I would like to acknowledge NASA, ECMWF, and KNMI for providing freely accessible datasets for my research work. I would like to thank all the staff members of WREM department at ITC for enriching us with their valuable knowledge during the period of study here at ITC. To all my WREM fellow colleagues, I would like to express my appreciation for the friendship and support during last 18 months. My sincere thanks to my parents and family for their continuous moral support and encouragement to complete this research program. ii TABLE OF CONTENTS Abstract.................................................................................................................................................................... i Acknowledgements ................................................................................................................................................ ii Table of contents .................................................................................................................................................. iii List of figures ......................................................................................................................................................... v List of tables ......................................................................................................................................................... vii List of Acronyms ................................................................................................................................................ viii 1. Introduction ................................................................................................................................................. 1 1.1. Drought Assessment ...................................................................................................................................................1 1.2. Evapotranspiration Estimation .................................................................................................................................2 1.3. Twente Drought Monitoring .....................................................................................................................................2 1.4. Problem Statement ......................................................................................................................................................2 1.5. Research Objectives and Questions .........................................................................................................................2 1.5.1. Specific objectives .............................................................................................................................. 2 1.5.2. Research questions ............................................................................................................................. 2 2. Theory ........................................................................................................................................................... 3 2.1. Drought .........................................................................................................................................................................3 2.1.1. Drought Classification ....................................................................................................................... 3 2.1.2. Drought Indices ................................................................................................................................. 3 2.2. Concept of Evapotranspiration ................................................................................................................................4 2.2.1. Conventional Methods ...................................................................................................................... 5 2.2.2. Remote Sensing methods .................................................................................................................. 7 2.3. Surface Energy Balance System (SEBS) ..................................................................................................................9 2.3.1. Determination