Deterioration of Coastal Freshwater Resources: Future Projections and Analysis

Anthropogenic climate change being an undeniable part of the 21st century is a rather new concept. Being believed to have started in the 1950s with the increasing CO2 emissions, the persistent increase of CO2 levels is expected to further alter climatic patterns which in turn will have irreversible environmental consequences.

The hydrological cycle is affected greatly by climate change as it has an active relation to changing means of climate including precipitation and evapotranspiration. With the rising urgency of climate change the regional alterations of wet and dry conditions thus changes in hydrological processes and water resources has become significant. A number of studies conducted to highlight the intensifying stresses on freshwater resources.

Coasts are amongst the most sensitive areas to climate change. Coastal aquifers being freshwater resources of utter importance are affected extensively by salinity intrusion, which is defined as the replacement of freshwater by saltwater. The intrusion of saltwater into coastal aquifer effectively reduces the freshwater levels. Changes in the climatic conditions would be expected to alter groundwater recharge and affect the availability of fresh groundwater. Increases in groundwater recharge shift the salinity interface seaward and decrease in recharge shifts it landward.

General circulation models are used by a number of studies predicting the future impacts of increasing CO2 levels on climatic alterations. A study conducted by Priyantha Ranjan, So Kazama and Masaki Sawamoto focusing on the results of Hadley centre GCM (HadCM3) along with two SRES scenarios; high emission (SRES-SA2) and a low emission scenario (SRES-B2), expressed the different results of climate change and population growth on coastal groundwater resources.

Precipitation, temperature, aridity

Precipitation, being an ever-changing part of the climate, is an integral part of the water balance and primary source of groundwater recharge. It is variable in time and space and future precipitation patterns are expected to affect fresh groundwater variability. Estimated rises in the temperature are expected to result in increases in evaporation, thus a rise in evapotranspiration which would have effects on groundwater recharge. As hydrological cycles and climate change possess advanced complexities in relation, a measure of aridity which is the ratio of mean annual precipitation to mean annual temperature. Aridity indexes are used as quantitative indicators of the water deficiency level within a region and express the effects of water and energy in a combined manner.

The study conducted by Ranjan, Kazama and Sawamoto has focused on the effects future projections of the precipitation, temperature and aridity would have on coastal groundwater aquifers and possible relations they might possess. The study focused on Central America, the Mediterranean, North Africa, South Africa and South Asia.

Projections for Low and High Emission Scenarios

The study estimated deterioration in fresh groundwater resources under both scenarios for the majority of the locations under the study. However, Africa and the Sahara region did not have an obvious decreasing trend associated with the coastal aquifers. While Asian and Mediterranean regions showed fluctuations in annual precipitation levels, there was a subtle increasing trend in Central America accompanied by a slightly decreasing trend in southern African regions. However, annual precipitation levels can be observed to have not resulted in a short term change in fresh groundwater resources in high emission scenario. While South African region shows short-term fluctuations projected for the low emissions.  A projected increase in precipitation for northern Africa/ Sahara region can also be observed accompanied by observations of long-term increases in fresh groundwater resources within the region. A conclusion stating no clear relationship between changing temperatures and fresh groundwater resources can be drawn from the observations.

Furthermore, while the high correlation between the precipitation levels and loss of fresh groundwater resources can be observed within the regions of the Mediterranean and South Asia, with correlation coefficients of 0.92 and 0.78 accompanied by 0.65 and 0.68 for high and low emission scenarios respectively. On the contrary, the precipitation variations related to fresh groundwater loss were small in North Africa. The correlation between fresh groundwater levels and precipitation was observed to be poor in general. The conclusion was drawn for both precipitation and temperature analysis led to the analysis of combined effects of both parameters; aridity index.

The aridity index and a reduction in the fresh groundwater levels have shown a negative correlation globally for both scenarios. However, the correlation was not observed to be present in northern Africa / Sahara region. Low aridity index corresponded to higher decreases in aquifer levels in Central America. Furthermore, due to higher mean precipitation and lower mean temperature values, the Mediterranean region had a lower loss of coastal groundwater resources compared to South Asia.

Conclusions

The relations between precipitation, temperature and changes in the fresh groundwater levels highlighted, aims to highlight the complexities of hydrological consequences caused changing the climate. While individually precipitation and temperature changes do not possess any power over fluctuations of the groundwater levels, aridity index is observed to have a negative correlation to loss of fresh groundwater resources globally.

While environmental factors retain a number of stresses over coastal groundwater resources when analysing future projections of climate change-related resource depletion, population change should also be factored in. Especially in South Asia deteriorating fresh groundwater resources coupled with the rising population are expected to upsurge the complexity of the of water stress. Increased domestic, agricultural and industrial demand of freshwater will only escalate through the years.

As presented by the means of science anthropogenic climate change has consequences that might be hidden from the bare eyes. With the rising populations along the coasts, coastal resources are in under undeniable stress which should be addressed with immediate effect. Along with the decrease of emissions, we must pursue environmental control of resource use to avoid future crisis. 

Scientific term definitions are available.