Organisation

PhD Defence Mr Fouad Alkhaier

Dept. of Water Resources

Title of defence

Shallow groundwater effect on land surface temperature and surface energy balance (description, modeling and remote sensing application)

Summary

Shallow groundwater usually characterizes low lands within watersheds. Besides, many newly  reclaimed irrigation lands suffer shallow water table conditions. Groundwater flow models and the management of irrigation systems can be greatly supported by satellite thermal recurrent measurements, provided that these measurements were capable of detecting the depth and the areal extent of shallow groundwater.  Such  measurements  have  additional  advantage  in  monitoring the shallow groundwater effect on surface energy balance, and in bringing that effect within land surface and climate models on more solid basis.

The objective of this Research is to explore and appreciate the different aspects and basic physical principles involved in the process of shallow groundwater effect on land surface temperature and surface energy balance, and to investigate the potential of remote sensing to delineate this effect. To reach the goal of this study, three paths were followed: in situ measurements, numerical simulations and remote sensing data manipulations.

The in situ measurements were conducted within Al-Balikh river basin in northern Syria. The study area represents a flat region of agricultural fields that suffers shallow water tables conditions. The field measurements included surface soil moisture and temperature measurements, water table depth readings, soil composition analysis, geologic maps and weather data collection. Variant numerical experiments were conducted to explore the processes that play a role in groundwater effect on land surface temperature and surface energy balance. The last path in this study involved using MODIS data and SEBS algorithm to inspect the spatial and temporal patterns of shallow groundwater effect on land surface temperature and surface energy balance in the study area.

Shallow groundwater affects thermal properties of the region below its water table. Moreover, it alters soil moisture of the zone above its water table which results in affecting its thermal properties, the magnitude of evaporation, albedo and emissivity. Hence shallow groundwater affects land surface temperature and the surface energy balance in two different ways; direct and indirect: The direct way (thermodynamic effect) takes place through groundwater distinctive thermal properties and affects heat propagation within soil profile. The indirect way is through its effect on soil moisture above water table and its related effects (i.e. evaporation, soil thermal properties of vadose zone, land surface emissivity and albedo). With the aid of numerical modeling the thermodynamic effect was separated out numerically from the indirect effect. It was shown that the presence of groundwater, through its distinctive thermal properties within the yearly depth of heat penetration, affects directly land surface temperature and the entire surface energy balance system thereby. In spite of its small magnitudes, highlighting the different features of the thermodynamic effect is useful to complete the understanding of groundwater effect. The interaction of the thermodynamic effect with the indirect effect may increase or decrease the upshot of the combined effect.

To know when and how groundwater effect takes place or whether it is possible to utilize currently operational satellites in its detection, the combined effect of shallow groundwater was simulated. In this simulation, the majority of the aspects through which  shallow  groundwater  affects  land  surface  temperature and  the various components of surface energy balance were taken into consideration.

The results show that shallow groundwater areas reflect less shortwave radiation due to their lower albedo and therefore, they get higher magnitude of shortwave radiation. When potential evaporation demand is high enough, a large portion of the energy received by these areas is spent on evaporation. This makes the latent heat flux predominant, and leaves less energy to heat the soil. Consequently, this induces lower magnitudes of both sensible and ground heat fluxes. The higher soil thermal conductivity in shallow groundwater areas facilitates heat transfer between the top soil and the subsurface which promotes greater provisional heat transfer in both vertical directions. i.e., soil subsurface is more thermally connected to the atmosphere. Nevertheless, the continuous heat exchange between the surface and the subsurface makes the deep soil temperatures come into equilibrium with surface and climate conditions. As a result, the upshot of ground heat flux in both profiles is very close to zero in the long run.

With regards to remote sensors’ capability of detecting shallow groundwater effect on land surface temperature, it was found that this effect can be sufficiently clear to be sensed if at least one of two conditions are met: firstly, latent heat flux effect is predominant due to the high potential evaporation, or secondly, soil volumetric heat capacity effect is strong due to the big contrast in air temperature between day and night.

The remote sensing data investigations showed that it is possible to map the effect of shallow groundwater on land surface temperature using the freely available satellite data like MODIS. Satellite measurements demonstrated a clear correspondence of surface temperature with water table depth day and night. Consequently, the various surface energy balance maps, calculated using SEBS and MODIS data, correlated well with water table depth.

Many factors played a role in the good results of remote sensing investigation. Firstly, the two major conditions were met in this day of investigation, i.e. high potential evaporation and high contrast in air temperature. Secondly, the surface soil moisture and water table depth conditions were fairly stable. Thirdly, the limited topographic relief and vegetation cover in the study area helped to avoid possible uncertainty sources in surface temperature measurements and SEBS estimates of energy fluxes. Finally, due to its imaging times and visiting frequency, bands diversity, sensor accuracy, precision and resolution, MODIS proved to be useful in this study. Yet, its spatial resolution was disadvantageous.

Possible finer resolution in future satellites may enable masking out the undesired effect of unrelated surfaces, and make the thermal mapping of shallow aquifers more precise. Advanced investigations of groundwater effect under vegetated and dynamic conditions are recommended for further research using remote sensing data and dynamic 3-D numerical simulations.

Biography

Fouad Alkhaier was born on January 24, 1973 in Damascus, Syria. He received his BSc (1997) and a post graduate diploma (2000) in Civil Engineering (Engineering management and construction Specialization) from Aleppo University, Syria. Soon after his university graduation he worked for the General Company for Land Reclamation, Ar-Raqqa, Syria as an executive Engineer in Asswedeah Irrigation and Drainage Project. In 1998 he worked in Civil Works Department of the General Organization of the Euphrates Dam (G.O.E.D.), Al-Thawrah, Syria. In this period he worked on computerizing databases and operations in Euphrates Dam and followed many training courses in PC maintenance and programming.

In the period between 2001 and 2003, he conducted his MSc research at the international institute of Geo-Information Science and Earth Observation (ITC), the Netherlands. His MSc specialization was Watershed Management, Conservation and River Basin Planning specialization. He used Remote Sensing and Geographic Information Systems in the field of Spatial Hydrology and Water Resources Management. His MSc thesis "Soil Salinity Detection Using Satellite Remote Sensing" has been referenced frequently in the pertinent international works. The ASTER index he introduced for soil salinity detection was used by the "Anthropology Analytical Cartography and GIS Lab" at the Pennsylvania State University, and was also used by "RTI International" in Iraq. During the working visit of the Crown Prince of the Netherlands "Willem Alexander" to ITC on 29 October 2002, Fouad was chosen to give a guest lecture to HRH on the Unique Opportunities of Remote Sensing in Water Management of River Basins. Fouad participated in developing an educational program "Management of International River Basins and Water Related Conflicts", which was presented in International Seminar for Students in Netherlands, The Peace Palace, the Hague, in March, 2002.

After his MSc graduation he worked for Water Resources Studies Department, General Organization of the Euphrates Dam (G.O.E.D.), Al-Thawrah, Syria and has an essential role in introducing Remote Sensing and Geographic Information System technology to the Department, and in establishing the cooperation between G.O.E.D. and the General Organization of Remote Sensing in Damascus.

In 2005 he started his challenging PhD topic in linking remote sensing to groundwater systems and concluded his research with his thesis entitled "Shallow Groundwater Effect on Land Surface Temperature and Surface Energy Balance: Description, Modeling and Remote Sensing Application". In his PhD thesis he showed how shallow groundwater systems affect soil surface temperature, moisture and Surface Energy Balance. Also, he demonstrated how it is possible to use thermal data of current satellites to detect that effect. During his PhD Fouad carried out abundant fieldwork in Al-Balikh Basin in Syria and participated in different international field campaigns like AquiferEx in Tunisia, 2005 and EAGLE in the Netherlands 2006. He also participated in the supervision process of MSc students. In 2010 and 2011, Fouad was invited to review articles in ISI journals like: "Remote Sensing of Environment" and "Land Degradation & Development". In 2007, he participated in the EAGLE Campaigns Final Workshop, European Space Agency center, Noordwijk, the Netherlands and presented a presentation on "Soil moisture field observations over the Cabauw grassland". And in 2009, he participated in the European Geosciences Union General Assembly, Vienna by a presentation on "The effect of shallow groundwater on soil temperature and soil heat flux near land surface". Besides, he participated in the ITC PhD day in 2008 and 2010.

Al-Khaier, F. and Su, Z. (Promotor)  (2011) Shallow groundwater effect on land surface temperature and surface energy balance : description, modeling and remote sensing application. ITC Dissertation 198, ISBN: 978-90-6164-322-7.

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