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III(i) Water and Crops
Published in Richard J. Chorley, Introduction to Geographical Hydrology, 2019
Water moves in the plant as a continuous stream from the root hairs to the leaf surfaces in response to the cell diffusion pressure-deficit gradient. This gradient is made up of a chain of increasing D.P.D.s, and the D.P.D. is thus a measure of the capacity of a saline cell to absorb water, either from an adjacent (generally less saline) cell or from soil water. As equation (1) shows, the D.P.D. is not entirely a function of the cell osmotic potential, and water may pass between cells having equal osmotic potential (i.e. salinity), providing the cell-wall pressures are different. The cell-wall pressure is largely a function of the extent to which the cytoplasm is forced against the elastic cell wall by changes in the water content of the vacuolar sap. Cells can lose turgidity either by plasmolysis (see later) or by wilting. Wilting occurs whenever evaporation takes place from leaf or stem surfaces faster than water can be supplied to the cells, such that the vacuolar sap decreases, reducing the cell-wall pressure, causing the plant to droop.
Machine learning based groundwater prediction in a data-scarce basin of Ghana
Published in Applied Artificial Intelligence, 2022
Ebenezer K. Siabi, Yihun Taddele Dile, Amos T. Kabo-Bah, Mark Amo-Boateng, Geophery K. Anornu, Komlavi Akpoti, Christopher Vuu, Peter Donkor, Samuel K. Mensah, Awo B. M. Incoom, Emmanuel K. Opoku, Thomas Atta-Darkwa
The seasonal trend analysis showed (Figure 3) that higher PET may occur in March before the onset of rains. However, the trend decreases as the major and minor rainfall seasons progress due to the shift of the Inter-tropical Discontinuity (ITD) toward the north in early March (Osei et al. 2019). This may be due to an increase in humidity and monsoonal clouds that reduce PET by reducing evaporative demand. The results showed that PET consistently reduces during the rainy season from June to September with minor increases in the dry season. The PET values were found to increase considerably from southern Ghana to the North due to increased rainfall and temperature (Kabo-Bah et al. 2016). This conforms with the study of (Carrier et al. 2008) which found similar south to north increasing PET trend in Ghana. Rainfall, for instance, plays a major role in explaining uncertainties in the estimation for PET. However, rainfall decreases significantly from north to south in Ghana. This conforms with the study of (Carrier et al. 2008) which found a south-south-west to north-north-east PET trend in Ghana. Rainfall varied significantly from northern to southern Ghana (Figure 3) and this was also reported by (Anayah et al. 2013). Therefore, an increase in PET, combined with variations in precipitation has the potential to modify the hydrological cycle especially GW recharge of any region (Rodríguez-Huerta, Rosas-Casals, and Margarita Hernández-Terrones 2020). Since shallow GW storage serves as the main source of water for plants with a deep root system, the increase in PET may deplete this storage. This, therefore, may cause wilting to most plants, especially natural vegetation and grasses. The water shortage and/or drought situation may get worse in the basins which are located in northern Ghana since forested trees with deep roots may use the shallow groundwater during the dry season (Osei et al. 2019). As a consequence, all the major dimensions of food security (i.e. availability, accessibility, utilization, and stability) and livelihoods may be at risk. For instance, the Upper East region has 21% of the consumption budget for food compared national average of 8% (GSS 2010).