Q & A –
Rajan Mungra – Director, Mauritius Meteorological Services
‘Forecasting weather in the tropics is very challenging. It is much harder when it comes to a small region of the size of Mauritius’
Following the publication of the Summer Outlook 2015-2016 by the Meteorological Services, we have thought it fit to seek some clarifications form Mr Rajan Mungra, Director of of the Mauritius Meteorological Services. They relate essentially to the methodologies used to make weather forecasts and the factors that influence the weather and climate generally, many of which are beyond human control. Also raised are issues of climate variability in a small place like Mauritius, and therefore the difficulty of making real time predictions.
* We learn from the latest Metrological Services’ Summer 2015-2016 Outlook that “heavy and/or torrential rainfall leading to flash floods, violent thunderstorm as well as electric storms, heat wave with high temperatures lingering for days and explosive intensification of cyclones may occur” during the coming months. It might not be possible to go into the details here, but can you tell us in a nutshell how you work out your forecasts and reach those conclusions?
Rajan Mungra: Long range forecast is based mostly on Numerical Weather Prediction models. Models use a wide spectrum of data on atmospheric parameters such as air temperature, pressure, sea surface temperature, humidity, etc., to generate the forecast based on the said parameters at different time scales.
The current state of the atmosphere and the regional features together with the forecast from the specialized centres are considered and compared with the long-term climatology. Such analyses reveal the state of the climate and the trend if any at the global and regional scales. The result can then be used to produce an outlook of the season.
Mauritius Meteorological Services do not own and run Numerical Weather Prediction Models as these require supercomputers and massive investment in terms of both human and financial resources. These are operated by specialized International Meteorological Centres. The products are made available to all other meteorological services under the aegis of and protocol established by the World Meteorological Organization (WMO) .
The main predictors analyzed are:
• EI Nino/ La Nina /Southem Oscillation Index (ENSO)
• Quasi-biennial Oscillation (QBO)
• Madden Julian Oscillation (MJO)
• Current state of the oceans
• Arabian high
• Indian monsoon activity
• Large-scale convective activity along the Inter-Tropical Convergence Zone (ITCZ)
• Axis of the Mascarenes subtropical anticyclones
• Indian Ocean Dipole
• Mean sea-level pressure anomalies during previous winter
• Mean temperature patterns during previous winter
• Cumulative rainfall over Mauritius during previous winter
• Convective activity over the islands of the South West Indian Ocean; and
• Upper level winds
* We presume that the Mauritius Meteorological Services are today better equipped both in terms of hardware and collaborative agreements with other foreign Met agencies for weather forecasting purposes. How much of what our Met comes up with in terms of forecasts presently in a place like Mauritius is dependent on the one hand on the input of science and technology and on the other on the human factor?
Meteorology and the science of weather is not bounded in time and space. Weather and the atmosphere are continuously observed both by man and remote sensing equipments like automatic weather stations, radar and satellites. Man-made observations as well as those made by remotely located instruments are disseminated worldwide and in real time.
A lot of information and data is shared everyday through the Global Telecommunication System put in place by WMO. Meteorological satellites observe the earth from space and are an important platform for monitoring the evolution of weather systems both on land and over the oceans.
Meteorological personnel are trained to observe weather. Instruments can measure and record meteorological parameters like wind, temperature, pressure, etc., but cannot replace human observers. Certain parameters can only be observed by human observers for example the type of clouds, the prevailing significant weather among others. Maintenance and calibration of instruments can be performed only by human beings. Meteorologists analyse the observations, data and all other available information to produce weather forecasts.
Forecasting weather in the tropics is very challenging. It is much harder when it comes to a small region of the size of Mauritius because of the variability of climate over the island, for example on a given day at a given time temperature may change from 32°C in Port Louis to 26°C in Curepipe. While on certain days it rains over the central plateau but the coastal areas remain dry and sunny.
In spite of all the available technology, human intervention is essential for monitoring and forecasting weather.
* Does the input from foreign Met agencies weigh heavily in the formulation of your forecasts?
As mentioned earlier weather observations and meteorological information have to be shared for a better analysis and monitoring of prevailing weather systems. Mutual collaboration and reliable data are the key factors for a successful forecast.
Please note that the national weather service of any country is the sole authority responsible for the issuance of weather forecast and severe weather warning for its jurisdiction.
This outlook has also considered the conclusions of the Southern Africa Regional Climate Outlook Forum (SARCOF) and model products from Global Producers of Long Range Forecast (GPLRF).
The list of GPLRF are as follows:
– European Center for Medium Range Weather Forecast (ECMWF)
– EUROSIP multi-model seasonal forecasting system
– United Kingdom Meteorological Office (UKMO)
– International Research Institute (IRI), USA
– Australian Bureau of Meteorology (BoM)
– National Center for Environmental Prediction (NCEP), USA
– Japan Agency for Marine-Earth Science Technology (JAMSTEC)
– Global Forecasting Center for Southern Africa (CSAG)
* Your Summer 2015-2016 Outlook also reveals the temperature “slightly warmer than usual” and likely to exceed the monthly average by more than two degrees Celsius in some locations. Maximum temperatures may reach 36 degrees Celsius at Port Louis. Would you say that this is quite normal given the pattern noted during the past couple of years?
Analyses of temperature recorded at Mauritius and its outer islands show a definite warming trend. Average temperature at all stations is rising at the rate of 0.15°C per decade and has risen by 0.74 to 1.2°C when compared to the 1961-1990 long-term mean. At some urban stations the temperature has risen by even greater amounts.
Similar warming trends have also been observed at the outer islands like Rodrigues, St Brandon and Agalega. The temperature at Agalega is rising at the rate of 0.11°C per decade. Temperature at St Brandon and Rodrigues has warmed up by 0.5 to 1.0°C.
The Intergovernmental Panel on Climate Change ( IPCC) also points towards a rising trend in the mean global temperature.
* What about the effects of climate change on the evolution of weather conditions in Mauritius generally? Is it measurable at this stage?
The nature of rainfall observed in recent years shows a changing trend with rainfall being of higher intensity and of short duration resulting in inland flooding and flash floods. Further, the strong rainy spells are being followed by a longer period of dryness. Rising temperature causes winter to be less harsh and summer more uncomfortable, with prolonged periods of days with above normal temperatures.
October is usually the driest month of the year for Mauritius with only a mean of 74mm of rainfall; however during October 2009 we had an all time record with 342% of the Long Term Mean (LTM). Similarly, this October in Rodrigues we just had well above normal rainfall during the first fortnight causing flash flood.
Storms/cyclones are intensifying at a faster rate and are getting more intense. We are having rainfall of high intensity in a very short period of time followed by a long period of dryness.
These confirm the effect of climate change climate variability. We expect that these extreme events will occur more regularly especially during peak summer months.