Comparison of seasonal total water storage variations from GRACE with groundwater levels, streamflow and soil moisture in southern Laos

POSTER ASEAN-EU Science, Technology and Innovation Days 2016, 10-12 May, 2016, Hanoi, Vietnam Comparison of seasonal total water storage variations from GRACE with groundwater levels, stream flow and soil moisture in Southern Laos Sinxay Vongphachanh Ph.D Student, School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology, Sydney, Australia Contact email: [email protected] Abstract The Gravity Recovery and Climate Experiment (GRACE) gravity satellite program was launched jointly by the National Aeronautics and Space Administration (NASA) of the United States and the German Aerospace Centre (DLR) in March 2002 to measure changes in the earth’s gravity field (Tapley et al. 2004). The movement of mass in surface water, soil water and ground water causes these changes. GRACE measurements are processed mathematically to extract estimates of total water storage (TWS) expressed as equivalent water height (EWH) with a spatial resolution of about 200,000 km2. In 2013, a new website for GRACE was developed by The Australian National University (ANU) using the spherical harmonic fields of the French Groupe de Recherche en Géodesie Spatiale (GRGS). This website provides a Data Visualisation Tool (DVT) by which users can estimate the EWH in a user specified region (polygon) or point with a spatial resolution of about 62,500 km2. GRACE data has been widely utilised to determine the variations of groundwater storage in many countries. However, this has not yet been implemented in Laos. Therefore, the main objective of this study is to investigate the feasibility of applying GRACE satellite data to estimate total groundwater storage in Southern Laos by comparing time series data of GRACE-derived TWS with groundwater levels, streamflow observations and soil moisture. A basin scale of about 25,000 km2 was utilised to investigate the GRACE-derived total water storage correlation with in situ groundwater levels and measured streamflow in southern Laos, one of the main target areas for agricultural development. The total groundwater availability in this area is currently not yet known exactly. This study presents the first direct comparison of total water storage derived from GRACE satellite mission with in situ hydrological monitoring. Monthly time series of soil moisture derived from the Global Land Data Assimilation System (GLDAS) and TWS drawn from GRACE between November 1, 2011 and April 30, 2013 are compared with groundwater levels from a piezometer network in Sukhuma district and Mekong River flow at Pakse hydro-meteorological station in Champasak Province, Southern Laos. Moreover, seasonal soil moisture maps derived from GLDAS are also compared with surface soil, land use and vegetation cover maps. The results illustrate that the GRACE-derived TWS agrees with the on-site groundwater table and streamflow measurements. In addition, comparison between soil moisture derived from GLDAS and measured groundwater table elevation in Sukhuma district and flow at Pakse station demonstrates similar seasonal fluctuations. The comparison between seasonal soil moisture maps and surface soil and vegetation maps shows that the highest volumes of soil moisture are usually found in Shrub land areas underlain by sandy loam soils. These preliminary results could be useful for estimating total groundwater storage variations and availability from GRACE data for Sukhuma district and Southern Laos in the future. Keywords: GRACE, GLDAS, Seasonal variations, Total Water Storage, Soil moisture, Groundwater levels, Southern Lao

Assessment of groundwater potential in data scarcity situation in southern Laos

University of Technology Sydney. Faculty of Engineering and Information Technology.Water is a vital natural resource that is needed for the sustainability of the hydro-environment and also for socio-economic development. In many developing nations, however, data necessary for assessing the available water resources and for planning the sustainable utilisation of these resources are lacking. Arising from increased population pressures in the Sukhuma District of Southern Laos, there is a need to assess the available water resources. Of particular concern is the interaction between surface water and groundwater together with the implications of this interaction on assessing sustainable water usage. The focus of the research presented herein is the utilisation of available data to assess the seasonal interaction of surface water and groundwater in the Sukhuma District. In addition, a water balance model was developed to enable the assessment of the sustainable water resources available for anthropogenic activities. These research activities can be expressed as data-mining of the available data for information. The available field data comprised short-term rainfall records, streamflow records, and groundwater levels collected over non-consistent time periods; in other words, no period contained data from all three sources. This limited field data was supplemented by remotely sensed data. However, the scales of the remotely sensed data and the field data differed, requiring down-scaling of the remotely sensed data. Data from the Gravity Recovery and Climate Experiment (GRACE) and from the Global Land Data Assimilation System (GLDAS) database were used for this purpose. It was found that the remotely sensed data could be down-scaled to be consistent with the region of interest. Additionally, it was found that there was good agreement between the characteristics of the interaction between the surface water and groundwater predicted by both the water balance model and the remotely sensed data. Arising from the analysis of this interaction, it was found that groundwater recharge in Sukhuma District was 3 – 4% of annual rainfall with a lag of two to six weeks (average 3 weeks) between the wet season start and a rise in groundwater levels. As shown in this research, non-traditional and traditional data sources can be combined in a manner leading to extraction of the available information in an efficient manner

GRACE detection of seasonal variations in total water storage in southern Lao PDR

POSTER GEOINDO2015, International Conference, “Geology, Geotechnology and Mineral Resources of Indochina”, 23-24/11/2015, Khon Kaen, Thailand GRACE detection of seasonal variations in total water storage in southern Lao PDR Sinxay Vongphachanh1 and William Milne-Home1 1School of Civil and Environmental Engineering, Faculty of Engineering and Information Technology, University of Technology, Sydney, Australia Contact email: [email protected] Abstract In 2013, a new website domain for the Gravity Recovery and Climate Experiment (GRACE) was developed by the Australian National University. This website provides a Data Visualisation Tool (DVT) by which users can estimate the equivalent water height (EWH) from a user specified region (polygon) or point. However, this website does not explain clearly enough about the precision of areal and point data derived from the DVT. Therefore, this study investigated the GRACE data detection of the total water storage (TWS, expressed as EWH) fluctuation in wet and dry seasons in southern Lao PDR. A basin scale of about 25,000 km2 was utilised to investigate the GRACE detection of TWS changes in southern Lao PDR, one of the main target areas for agricultural development. The total water availability in this area is currently not yet known exactly. This study compares the values of GRACE EWH derived from an area of 25,000 km2 with EWH points and observed stream water level data of Mekong River at Pakse hydro-meteorology station, Champasack province. Additionally, this study also compares the values of GRACE EWH point derived from different soil types and different land-use types. The results suggest that the GRACE can detect the seasonal flux of EWH and the extreme flood events in southern Lao PDR. It can be concluded that GRACE data can be used to estimate the total groundwater storage, surface water storage and soil moisture in southern Lao PDR. The proportion of soil and land use types could have a high potential influence on the EWH values. Keywords: GRACE, Seasonal variations, Equivalent water height, Total Water Storage, Southern Lao PD

Regional assessment of groundwater recharge in the lower Mekong Basin

Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations

Regional Assessment of Groundwater Recharge in the Lower Mekong Basin

Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations