Changes in the Global Water Cycle

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Introduction

Evidence does exist of the rise in the global mean surface air temperature in the twentieth century. More so, even if there are several uncertainties about the level of climatic change in the future, several types of research carried out show that in the future, global warming is quite likely. Among these scientists, we have some of them who believe that climate warming will bring about increased evaporation and precipitation which will then result in the increase of velocity of the water cycle. The acceleration of the water cycle could have some effects on the availability of the water resources and may in turn result in a rise in the occurrence and the strength of the tropic storms, droughts, floods, and the intensification of global warming in the course of the water vapor response (Thomas, 1).

According to the European Commission (1), an American researcher tried to study the probable connection involving global warming and the amplification of the water cycle, projected previously by other scientists. The scientist carried out a review of the present condition of science concerning past patterns in hydrological variables including precipitation, rivers flow, soil moisture among others so as to examine the feedback of the water cycle to the past and future climatic changes. The main characteristic of this research is that it involves fresh insights linking to the world continental stream flow, tropospheric water vapor, trends in glaciers, evaporation, and evapotranspiration. The researcher found out that, on global average, precipitation had been said to be risen by about two percent within a period of almost one hundred years beginning from the year 1900 up to the year 1998. More so, the rise in precipitation on land has been linked to the rise in the main rivers in several regions of the world. An examination of the patterns in continental flow in the main rivers between the year 1910 and the year 1975 realized a rise in the flow of approximately three percent. A more recent examination done again of such patterns for the period ranging from the year 1920 up to the year 1995 established a rise in the streamflow in the course of the twentieth century. Genio, Dai, and Fung (1) also comment on the issue of precipitation. They concur that the impact of the future global warming will be felt on precipitation trends and there will be recurrent droughts and floods.

More so, according to the European Commission (5), this scientist gave a report that the last half of the twentieth century realized amplification in the soil moisture, evapotranspiration, water vapor as well as ice buildup on mountain glaciers. Even if the recent researches have given a suggestion about a connection between patterns towards warming sea surface temperature and hurricane strength in the Atlantic, his research gave a suggestion that the experimental data to this time do not, without fail, support a rise in the rate of recurrence of tropical floods and storms.

Nevertheless, there are considerable uncertainties concerning the patterns in the hydrological and climatic variables due to the very variable excellence of the information and the regional variations and occasionally ambiguous results. Despite the uncertainties, the observed pattern in most of the variables examined gives a suggestion that global warming may actually have amplified the global hydrological cycle during the twentieth century. Because of the prospective effects of such a variation of the human life, it would be quite vital to bring about the improvement in the ability to check and forecast the impacts of altering the global water cycle.

Observed trends in precipitation

Other than the changes in temperature itself, conceivably the most significant prospective impact of global warming in time to come will be this global warming effect on global precipitation trends and recurrence of extreme droughts together with floods. Changes in precipitation may not just be a result of global warming but this may affect global warming also. A unique characteristic of this warming that was noticed in the previous century is that there has been warming of the temperatures in the course of the nighttime than during the daytime. This brings in some advantages in agriculture since the unfavorable frost may occur less frequently. But on the other hand, there may be adverse effects on the growth of some plants and cause the crop pests to thrive.

Soil Moisture

There exist a general small wetting pattern in the global soil moisture brought about by the rising precipitation, that is weighted by positive soil moisture patterns over the Western hemisphere and particularly in North America. But there are variations depending on the region. In West Africa, there is drying overdue to the reducing Sahel precipitation. Europe seems to have not experienced great changes in the soil moisture and this also applies to other parts like Southern and southeast Asia.

Runoff and streamflow trends

Following the climatic change, it is projected that by the year 2050 there will be an increase of between 10 and 40 percent in runoff in North America, Eurasia, eastern equatorial Africa and the La Plata basin. There will be a decrease of between 10 to 30 percent in the runoff in regions like Southern Africa, Southern Europe, Western North America, and the Middle East (Milly, Dunne and Vecchia, 1).

Groundwater trends

The changes in climate are experienced through changes in the hydrological system. Groundwater is the number one store of freshwater that can be accessible but it still remains chiefly marginal to the present analyses and discussions of climate change adaptation (Anonymous, Groundwater and climate, 1). The observations on the groundwater levels show that recharge volumes may change in considerable terms from one year to the other in relation to the changes in climate.

Trends in reservoir, lake, and wetland storage

In the last decade, there have been suggestions that the occurrence of drought in key regions of the world may have brought about a reduction in global reservoir storage. The overall area of lakes has experienced an increase in the continuous permafrost zone by about 12 percent. On the other hand, there has been a reduction in the isolated permafrost areas of western Siberia by 11 percent. Considering the case of wetlands, it is estimated that about fifty percent of the wetlands are found in the high latitudes. There is fear that permafrost dilapidation may cause wetlands to be exhausted and their place be taken by grasslands and this can cause a very grave impact on the global carbon cycle and likely responses to global climate change.

Trends in glaciers

The latest research indicates that most glaciers are getting thinner especially in Greenland and Antarctica implying that more water now is in the sea and there is less frozen water on the land. These glaciers are as well flowing at a higher rate than in previous times and their rate of shrinkage is seemingly under acceleration. If the present trends persist, most of the glaciers will completely disappear.

Snow trends

There has been a decrease in the average snow extend of 3.75 million square kilometers in the Northern hemisphere within a period of the past thirty-nine years. This decrease has mostly been occurring during the month of June and July. In the Southern hemisphere, there has been not much significant change. The reduction in the snow, as well as ice cover, brings about increase in the rate of warming.

Changes in evaporation and evapotranspiration

Changes that are long-term in evaporation and prospective evapotranspiration can have intense impacts on hydrological processes and at the same time on the performance in agriculture. Both pan evaporation and potential evapotranspiration have gone down in previous years, especially in the case of India. Warming that will come in the future is seemingly likely to bring about a general increase in potential transpiration although this increase will not be uniform between seasons as well as regions. These changes will have noticeable impacts on environmental and economic well-being, particularly when these increases are not alternated with enough increases in precipitation.

Permafrost trends

A general increase in the permafrost temperature has been observed especially in northwest Canada, Alaska, Siberia and the northern part of Europe in the past more than a few decades. During this period, there has been a substantial warming.

Links between the Terrestrial Carbon and Water Cycle

The relationship between the shifting global water cycle and the carbon cycle can be associated with the climatic change. A significant part is played by the terrestrial biosphere in the climate system of the earth since it has taken approximately a quarter of the anthropogenic carbon emissions in the course of the twentieth century. It has not yet been established the time the biosphere can still go on taking in the carbon from the atmosphere at this particular rate. Researches have shown that the rate at which carbon can be taken up is dependent on the land use and hydrologic state. However, some of the observations in the researches have been clear while others have not been very clear in the associations of patterns in both local and global carbon budgets with climate and hydrological factors. Since water has different roles in every stage of the carbon cycle, it is quite necessary that each stage be observed separately. The largest amount of the terrestrial carbon is found in soil and in the vegetative biomass found above the ground. Basically, carbon finds its way into the environmental compartments through the process of photosynthesis in plants and may leave through the process of respiration, transfer of carbon to the lakes and rivers and the alterations of the land use.

As much as the hydrological processes are vital in all stages of the carbon cycle, the patterns in the carbon cycle are only at times strongly connected with patterns in the hydrological cycle. Availability of water may turn out to be a limiting factor as other climatic factors adjust for some ecosystems. Direct observations of carbon fluxes and storages have not often been made over appropriate time periods or regions for significant patterns to be identified but strong confirmation can still exist to indicate possible impacts of hydrologic patterns on the carbon cycle.

Is The Hydrologic Cycle Accelerating?

According to Miller (1), the hydrological cycle is accelerating. The hydrological cycle comprises water fluxes and stores in the air, oceans, lakes, and parts of land. The volume of water in total in the system of the earth is about (1.36 × 10⁹) KM³ of which about 97 percent is stored by the oceans, about 2.9 percent is stored in the rivers, lakes, ice, snow, and as underground water and only about 0.1 percent is found in the atmosphere. The water cycling involves transportation of atmospheric water vapor as well as precipitation, evaporation from the earths surface, transpiration from the plants, permeation of water into the earth, permafrost, surface runoff, water found in the oceans, snow glaciers, and underground water.

The hydrological cycle is connected directly with the quantity of absorption in the atmosphere together with the reflection and transmission of the received energy of the sun and also the quantity of the longwave radiations given out from the surfaces of land and oceans. The gases that occur in a natural way have played a major role in the regulation balance of the atmospheric radiation and the resultant temperature. Yet, the rising rate of emissions of carbon dioxide as well as other gases that absorb heat like methane has altered the balance bringing in warming of the lower atmosphere.

According to Miller (7), while there is continuous warming of the troposphere with an increase of between one degree and six degrees Celsius of the temperature in the course, this will make the acceleration of the hydrological cycle be clearly seen. Among the most responsive mechanisms of the hydrological water cycle is the alteration in the water vapor in the atmosphere and the subsequent alterations in the distribution of precipitation, its type together with its distribution. Air masses that are warmer have the ability to carry more water vapor causing events of excess precipitation which are in the form of floods that occur more often and also droughts that are prolonged also result. This alteration in the level of precipitation and water vapor brings an effect whereby there is a great likelihood that dry areas may become drier while wet areas may become wetter.

Assessing Future Impacts of Climatic Change

The accelerated hydrological water cycle brought about by global warming could have significant impacts on water availability. According to the United Nations Global Impact report, the change in climate will bring about an effect on the scarcity of water and the sustainability of its supply (Anonymous, 2). According to this report, climatic change will cause an increase in the shortage of water as a result of alterations in precipitation trends and amount. This effect will be felt mostly in the mid-latitudes and sub-tropics and these areas are expected to become drier. More so, there will be a reduction in the capacity of water storage from melting of glacier and as a result, there will be a reduction in the lasting availability of water for the people who stay in the glacier-fed river basins comprising of parts of countries like India, China, and the United States of America. There will also be a rise in the susceptibility of ecosystems due to the rise in the temperatures, variations in the precipitation trends, weather events that are severe will be more often, and longer droughts. There will also be an effect on the dependability and capacity of infrastructure for providing water as a reason of flooding, severe weather, and rising sea level. Many of the plants that deal in treating and supplying water were not designed to stand the anticipated rise in the sea level and the increased occurrences of extreme weather.

This report also indicates that climatic change will bring about an impact on the quality of the water. Increased precipitation together with flooding will bring up the level of erosion and this in turn leads to pollution of water sources. There will be contamination of coastal surface and groundwater sources as a result of the rising sea level which in turn will lead to saltwater intruding into the rivers and the groundwater reserves. In addition, there will be a rise in the temperature of water which will bring about an effect of enhancing the growth of more algae and bacteria bringing about water contamination (Anonymous, Climatic change and the global water crisis: What business need to know and do. United Nations Global Impact, 2).

Conclusion

So far, from the discussion, it can now be clearly seen that the changes in the climate brought about by global warming have a much bigger likelihood of impacting negatively on the global hydrological cycle. The acceleration of this cycle brings in unfavorable conditions for life on earth such as extreme climatic conditions. Therefore, measures must be taken to deal with the problem of global warming to minimize climate change and this will, in turn, solve this problem.

Works Cited

Anonymous. Climatic change and the global water crisis: What businesses need to know and do, United Nations Global Impact. 2009.

Anonymous. Groundwater and climate. Commission of ground water and climate change. Web.

European Commission. Changes in the Global Water cycle linked to Global Warming, European Commission DG ENV News Alert issue 22. 2006. Web.

Genio Del Anthony, Dai Aiguo, Fung Inez. Precipitation Trends in the Twentieth Century, Goddard Institute for Space Studies. December 1997. Web.

Huntington G. Thomas. Evidence of intensification of the global water cycle: Review and synthesis. Journal of Hydrology 319 (2006) 8395. Web.

Miller Norman L. Hydrological consequences of global warming. Lawrence Berkeley National Library.

Milly, Dunne and Vecchia. Global pattern of trends in stream flow and water availability in a changing climate. Nature Publishing Group.

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