DISCUSSION: When people think of tropical cyclones, most would quickly think of open ocean genesis situations and favorable environmental conditions which would keep an organized low-pressure system intact. After all, any tropical low is essentially a self-sustaining heat engine that transports heat from the tropics and poleward towards the mid-latitudes (i.e., regions located between 10 and 30 degrees North and between 10 and 30 degrees South respectively). Many people generally tend to think that once a tropical cyclone impacts land, weakening of the core circulation tends to happen rather quickly. That greater rate of weakening is presumed to be due to greater friction with terrain that effectively disrupts the center of circulation and negatively affects both spiral rain-bands and core convection alike. But a generous void exists in the meteorological literature about tropical lows that form over land (i.e., those which form primarily over central and southern Africa).
Most commonly found during the heavier precipitation months (i.e., between December through March), these tropical low-pressure systems form over land as a consequence of moisture that is displaced from the intertropical convergence zone (ITCZ). More specifically, the ITCZ is an area of persistent deep thunderstorm activity that oscillates between the Northern and Southern Hemispheres depending on the time of year. Around this time of the year, high moisture content and instability generated by the release of latent heat in the mid-troposphere (i.e., between roughly 2 and 5 kilometers up) combine with a favorable wind shear profile to generate a cyclonic structure similar to what is observed across tropical ocean basins. Although peak surface winds are not as strong as those found in association with tropical storms over open waters (e.g., the strong core wind speeds which were observed with both Hurricane Irma and Hurricane Maria), some of these land-based cyclones can still have high winds that can inflict substantial wind damage. However, these systems are mostly known for their potentially copious amounts of precipitation and thus are considered high-impact events as flooding is the principal threat in this otherwise semi-arid region of Africa.
Fortunately, the development of such a tropical low-pressure system would likely weaken the grip of excessive heat impacting southwestern South Africa at a given point in time. In recent days, there have been confirmed observations for maximum temperatures over inland areas in excess of 38°C (100°F) and these same areas have been hit excessively hard by a long-lasting drought. This low-pressure system is expected to develop over Angola and slowly travel southward through Botswana and Zambia. Heavy (and very much needed) rainfall (i.e., on the order of 6 inches (or 0.16 meters) or more) is expected to fall over southwestern South Africa over the next 7 days. This heavy rainfall may also help to provide relief from the lengthy period of drought previously noted above. The photo attached above can be found at the following web address: https://www.eumetsat.int/website/home/Images /ImageLibrary /DAT_IL_10_01_24_A.html.
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© 2018 Meteorologist Brian Matilla and Meteorologist Jordan Rabinowitz
The dried up Theewaterskloof dam in Viliersdorp, South Africa. The single biggest dam supplying water to the metropole of Cape Town. [Source : Jon Kerrin]
Cape Town's drought and associated water restriction has officially gone up to the level of a disaster. The news of the drought crisis has spread across the globe, and the world is now paying attention to know the fate of the city. This drought has been caused by three years of very low rainfall, associated with increasing consumption by a growing population.
“Day Zero”, currently forecast for April 16, is the day when the taps will run dry in Cape Town. According to the latest data, dam levels for Cape Town are 26.3% as at January 29, 2018. The day has been approaching faster– brought forward by the city's excessive consumption despite proactive measures like the implementation of water restrictions.
The four million inhabitants will be forced to collect a daily water ration of only 25 litres from 200 water collection points – barely enough for a two-minute shower.
How did this happen?
It has been a slow-motion crisis, triggered by three factors:
Some studies suggest that the possibility of extreme drought is increasing in the western part of South Africa. Future climate projections show a possible shift towards a drier, more drought-prone climate. This means that it is possible that man-made influenced climate change has contributed to the severity of the current drought, and even though it is an extremely rare event, similar droughts may not be rare in the future. On a positive note, there will still be wet years, but likely not as many.
What solutions are being implemented?
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©2018 Oceanographer Daneeja Mawren