1.4 Problem definition
Written by Abbas Farshad and Ali Abkar
Let’s start with the fact that climate change leads to more extreme weather conditions causing floods and droughts.
Probably you too asked yourself why again a post/report/book on drought. This is what we also asked ourselves initially, but soon we had the answer when seeing that there are still people, and worst of all some of the politicians, who do not believe in climate change.
The definition of drought is associated with the deficiency or absence of precipitation and/or groundwater circulation systems as compared to the typical situation. According to the World Meteorological Organization (WMO), “an area is affected by drought when the annual precipitation is lower than 60% of the normal values, at least for two consecutive years in more than 50% of its area”. Although it is true that annual precipitation is the main trigger of drought, its effects vary depending on the drought type (Fig. 1.1). No matter how much rain falls, the focus is put on how much of that rain is useful water (Smith, 2001).
Fig. 1.1: Different types of draught (after Keith Smith, 2001)
Effective rainfall (or precipitation) is equal to the difference between total rainfall and actual evapotranspiration. Effective rainfall is roughly calculatable by:
Effective Precipitation (mm) = (RAIN – 5) x 0.75
The function of effective rainfall increases with increased water-holding capacity in soil. The amount of water held and retained by soil depends upon its depth, texture, structure, and organic matter content, the finer the texture, the greater the storage capacity.
The type that limits crop production in the sandy soils is indeed the ‘agricultural drought’. “An agricultural drought occurs when soil moisture is insufficient to maintain average crop growth and yields”
The following problems were distinguished, using the technique of “problem tree analysis” (Fig. 1.2):
In addition to the above problems, drought may be considered the gateway to desertification considering its numerous effects on the environment, namely:
Drop of water table depth;
Decrease in river flow;
Water pollution;
Soil and water salinization;
Soil pollution by fertilizers;
Promoting soil erosion risk;
Promoting wild and forest fires risk;
Vulnerability of vegetation to other damaging agents such as pests, fires, wind, etc.
No doubt that a distinction should be made between a short drought when the rainfall in 1 to 2 years is below the average, and when the dry period is lasting for a decade or more (Kassas, 1999). Longevous drought occurrence is kept responsible for the collapse of cultures. Several researchers have argued that the Akkadian (2334-2218 BCE) and the Mayas cultures (The preclassical period lasted from about 2000 BC to about 250 AD) collapsed as a result of drought/ desertification (Diamond, 2005; Stromberg, 2012). For more info see https://www.agriwatch.nl/knowledge-center/historical-droughts, and https://www.agriwatch.nl/knowledge-center/news-international-aw .
It is a well-known fact that intensification of agricultural production and soil use and its management, industrialization, deforestation, and urbanization, directly and indirectly, affect soil quality, through using contaminants (heavy metals, pesticides), acidic atmospheric deposition, and excess nutrients (nitrogen and phosphorus), etc. The intensification and changes in land use may also contribute to physical soil degradation through erosion, depletion of soil organic matter, compaction, disturbance and sealing of soils (van der Veer, G. 2006).
Although not an easy job, drought can also be managed by following three principal elements, namely:
an early warning (forecast) mechanism,
societal preparedness, and
an enabling mechanism for providing support and relief to menaced communities (Kassas,1999).
Farm management under conditions of drought needs to be reconsidered. Farming actions are based on (statistical) predictive models and are hampered by economic and social means.
The drought itself and the effect on soil and crops can be highly local and periodic. The locality context in this study can basically be sought in soilscape-related [soil parent material, landform and (micro-) topography] variabilities. Farming on sandy (with variable texture and chemical composition) soils, veengronden (laagveen and former “hoge venen”), the recent reclaimed lands and “ruilverkaveling” are the key questions, not to forget the use of machinery and artificial fertiliser that has changed unsuitable land into economically viable farmland.
Moreover it is good to mention that droughts and heatwaves also impact human health.
References
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Save Soil: https://www.consciousplanet.org/
What is climate change? A really simple guide: https://www.bbc.com/news/science-environment-24021772
Drought emergency declared in northern Italy: https://www.bbc.com/news/world-europe-62046165
Japan swelters in its worst heatwave ever recorded: https://www.bbc.com/news/world-asia-61976937
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How the Middle East is suffering on the front lines of climate change: https://www.weforum.org/agenda/2019/04/middle-east-front-lines-climate-change-mena
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