University of Twente Student Theses
Assessing meteorological and vegetation drought indices against soil moisture measurements over Twente region, The Netherlands
Musila, Patience Katheo (2021) Assessing meteorological and vegetation drought indices against soil moisture measurements over Twente region, The Netherlands.
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| Abstract: | Drought events of high precipitation deficits have become rampant in the Netherlands in the recent years. The year 2018 was recorded as the worst drought with associated huge impacts on the economy, agriculture, and navigation industry. Drought indices (often unitless, and between 1 and -1) have provided a reliable way of quantifying the characteristics of droughts by comparing prevailing climatic conditions to their long term normal (mean). This research investigated the potential of meteorological drought indices (the Standardized Precipitation Index, SPI, and the Standardized Precipitation Evapotranspiration Index, SPEI) in combination with vegetation drought indices (the Normalized Difference Vegetation Index Anomaly, NDVI-A and the Normalized Difference Water Index Anomaly, NDWI-A) to quantify agricultural droughts as observed by anomalies of in-situ soil profile measurements in the Twente region, The Netherlands. These indices provided flexibility in detecting short term dry events that occur in meteorological and agricultural droughts at two given timescales (16-day and monthly). For meteorological indices, higher correlations of SPEI over SPI in relation to soil moisture anomalies, indicated the importance of incorporating the water demand component that corresponds to the role of soil moisture (provision of water vapor) which is not accounted for by SPI. For the vegetation drought indices, high correlations of NDWI-A over NDVI-A in relation to soil moisture anomalies, provided insight on the complex relationship between various leaf components (leaf water content and chlorophyll content (“greenness”) and soil moisture. When soil moisture anomalies were lagged backwards in months, SPEI yielded a higher correlation over SPI with a lag of one month. This illustrated that impacts of the water balance anomalies (high precipitation deficit, high temperatures, and increased radiation) are best observed in soil moisture after one month. The NDVI-A correlation illustrated a slight increase with a lag of one month indicating that observed vegetation “greenness” responds optimally to antecedent soil moisture conditions of one month. Conversely, the NDWI-A reduced its correlation with one-month lag but had a high correlation at zero-time lag. This illustrated that the leaf water content responds quicker to ongoing soil moisture variations without delay than observed “greenness”. The research concluded that SPEI and NDWI-A were the preferred drought indices for estimating agricultural droughts based on their high and quick response to soil moisture anomalies in Twente region. |
| Item Type: | Essay (Master) |
| Faculty: | ITC: Faculty of Geo-information Science and Earth Observation |
| Programme: | Geoinformation Science and Earth Observation MSc (75014) |
| Link to this item: | https://purl.utwente.nl/essays/88911 |
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