The PISSARO project

Summary presentation

The PISSARO project is led by Sylvie Malardel, meteorological engineer at Météo-France and researcher and animated by Hélène Vérèmes, post-doctoral fellow at LACy (Laboratoire de l’Atmosphère et des Cyclones, La Réunion, France). The PISSARO project (Intra-Seasonal to Seasonal Forecasts with AROme) focuses on atmospheric and oceanic forecasting at the subseasonal scale, i.e. with time scales ranging from 2 weeks to 2 months, for applications over the south-western Indian Ocean basin. This is a collaborative project for the valorisation of research data, developed and conducted in partnership with stakeholders mainly in Reunion Island but also in the Seychelles and other countries. It started in October 2020 and will last for 3 years until 2023. This project is co-financed by the European Union via an ERDF grant and the Réunion Region as part of the INTERREG-V OCEAN INDIEN 2014-2020 cooperation programme on an action linked to innovation and the exploitation of research databases.

Partners of the project

The project is led by the LACy, an academic research laboratory under the supervision of the University of La Réunion, the CNRS and Météo-France, specialised in tropical meteorology. It will be accompanied by a network of international scientific experts from the European Centre for Meteorological Forecasting (ECMWF, England), the french national school of meteorology (ENM, Toulouse, France) and other laboratories and institutes around the world. In addition to these academic actors, there are institutional partners. The project will benefit from the expertise of the meteorological service of Reunion Island through the DIROI (Direction InterRégionale de Météo-France pour l’Océan Indien), its climatological studies team and cyclone forecasters. DIROI is the operational weather forecasting service in Reunion and Mayotte and is a regional meteorological centre specialised in tropical cyclones in the southwestern Indian Ocean basin. The PISSARO project wishes above all to be oriented towards the applications of subseasonal forecasting for risk management, which is why the project has partners representing potential users. PIROI (Plateforme d’Intervention Régionale de l’Océan Indien) is attached to the International Relations and Operations Directorate of the French Red Cross, with a vast disaster risk management programme in the southwestern Indian Ocean. It represents a potential user for products that could be developed within the framework of PISSARO around tropical cyclones. The Seychelles Meteorological Authority (SMA), an operational weather forecasting service in the Seychelles, will allow the project to open up to other potential users of products developed around heavy rainfall and other meteorological or oceanographic situations. The PISSARO project is above all a collaborative project. Do not hesitate to consult the section Who are we? section for more details on the different partners of the project.

What is subseasonal forecasting?

Figure 1: Qualitative estimation of forecast skill based on the forecast range. Source: White et al (2017).

To understand the objectives of the project, it is necessary to understand the concept of subeasonal forecasting. Figure 1 shows the quality of the forecast as a function of the time scale of the forecast. Subseasonal forecasting (marked S2S in the figure) is aimed at time scales that have been little exploited until recently. The efforts of the scientific community have been mainly focused on :

– short- and medium-range weather forecasting (on the left of the figure), with time scales ranging from a few hours to a few days, for which the predictability depends very much on the quality of the estimate of the state of the atmosphere and the ocean at the start of the numerical simulation

– seasonal forecasting (on the right-hand side of the figure), with time scales of 3 to 6 months, for which the predictability depends on the evolution of the state of the ocean (sea-surface temperature), the mean state of the atmosphere and the ocean, and the external forcings.

Subseasonal forecasting falls between these two types of forecast. It can be interpreted according to the situation in terms of the occurrence of climate phenomena or anomalies. It requires special expertise. It bridges the gap between medium-term weather forecasting and seasonal forecasting. It must be able to provide users with a continuous chain of information to refine the elements entering into their decision-making process, which is what Figure 2 aims to illustrate.

Subseasonal forecasting and disaster risk reduction

Figure 2: Disaster risk management interventions along the time scale continuum of climate information. Source: UN Report (2019), modified from ESCAP (2017).

Figure 2 parallels the forecasting scales presented above with the time scale of decision-making for disaster risk management interventions. Subseasonal forecasting in the middle of the figure is between seasonal forecasting, which allows strategic decisions to be made several months in advance, and short- and medium-term weather forecasting, which allows operational decisions to be made a few days in advance. Subseasonal forecasting is concerned with tactical aspects. Subseasonal forecasting represents the missing link between seasonal forecasting and medium-term weather forecasting in the “Ready-Set-Go” concept proposed by the Red Cross Climate Centre and the IRI (International Research Infrastructure for Climate and Society) (Goddard et al., 2014). This concept provides a decision-making framework for risk management actors to progressively invest resources as the occurrence of the hazard becomes increasingly certain. Seasonal forecasting allows for readiness, emergency preparedness and response to be defined, preparedness and monitoring to begin. Subseasonal forecasting initiates decisions related to setting up (“Set”), strengthening preparedness and introducing forecast-based actions. And finally the short-term weather forecast gives the start (“Go”), it allows to activate the response. The interest of the PISSARO project is to evaluate the potential contribution of subseasonal forecasting to help decision-making for various applications, including disaster risk management.

S2S (Subseasonal-to-Seasonal Prediction Project)

The PISSARO project is part of a large-scale project called S2S established jointly in 2013 by the World Weather Research Program (WWRP) and the World Climate Research Program (WCRP), whose main objectives were to evaluate, improve and promote atmospheric and oceanic forecasting on the intraseasonal scale. It was decided that special attention would be paid to the risks associated with weather extremes (including tropical cyclones, droughts, floods, heat waves and monsoonal rainfall). The S2S project has deployed a very large database of subseasonal forecasts (up to 60 days) and ‘reforecasts’ (replay of past forecasts with the most recent version of the model). This represents a database of over 6 years of forecasts (in near-real time since 2015) and up to 25 years of reforecasts for a wide variety of atmospheric and some oceanic parameters, produced by 11 different forecast models. Why do we have to use 11 different forecast models? Not all models have the same performance. More details on the S2S project and the suseasonal forecasting database operated within the PISSARO project can be found in the S2S section.

The objectives of PISSARO

The first axis of PISSARO is the evaluation and improvement of subseasonal forecast data for the southwestern Indian Ocean and the second is their valorisation. The objectives of the project on data evaluation are the following:

– Evaluation of the S2S database for weeks 2 to 4 for tropical cyclone and extreme rainfall forecasting for the southwestern Indian Ocean

– Situation replay to assess whether the additional data available in the S2S database would have helped in better decision making for specific actions (as humanitarian action…)

– Contribute to the improvement of subseasonal forecasts in the southwestern Indian Ocean basin

Each region of the world has its own specificities. The more we know about the factors influencing the monthly forecast for the study region, the better the forecasts for that region will be.

Studies carried out by the S2S project scientists show that a signal can be found in terms of cyclonic activity at a monthly scale and particularly in weeks 1 and 2. These results allow us to optimistically consider the possibility of applying these data to develop products aimed at potential users and at risk prevention. The meteorological and oceanic risks to which the territories of the southwestern Indian Ocean may be exposed are described here. The user-oriented objectives of the project are as follows

  • Valorisation of S2S data through the development of application-specific forecasting and risk assessment products

◦ Highlighting the specification of forecasting and risk products for input to decision making

◦ Working closely with partner Météo-France (DIROI) for the development of risk products

– Setting up a sustainable internet platform to promote exchanges between the project partners and eventually offer forecasting and risk products

– Awareness raising and training of users on subseasonal forecasting and its specific applications for the southwestern Indian Ocean region

There are many hazard warning platforms available online and warning strategies deployed by national meteorological services or specialised institutions. But these tools are short range (0-3 days) and only a few are medium range (3-7 days). The objective of PISSARO is to adapt this type of product for the southwestern Indian Ocean to an subseasonal time scale. The products will be less accurate and subject to greater uncertainties but could potentially provide a probability of risk of tropical cyclone passage(s), heavy rainfall or other oceanic or meteorological situations for different predefined areas at a longer time scale.

In brief

The PISSARO project is an academic research project that started in October 2020 and will continue until 2023. The main approach is to study past data to :

– assess the quality of sub-seasonal forecasts for tropical cyclones and weather patterns

– develop user-friendly forecast products

This project focuses on the southwestern Indian Ocean basin which is often under-represented in global tools and whose specificities are not always taken into account. There are few warning products for risk management beyond a few days. The ambition to deploy early warning tools cannot be achieved without discussions between potential users and S2S experts. The potential users can specify the characteristics of the products to developed to be sure that those products would offer an advantage in decision making, and only the experts can assess the feasibility of these products.

Find all the news of the project on our blog, the various communications and as soon as possible the products in the dedicated sections.

List of bibliographic references

White et al. (2017). Potential applications of subseasonal-to-seasonal (S2S) predictions, Meteorological Applications, 24, 315-325.

United Nations, ESCAP, ASMC and RIMES (2019). Applying subseasonal-to-seasonal predictions to improve disaster risk reduction in South-East Asia: 10 key takeaways for disaster management authorities. (United Nations Publication, ST/ESCAP/2867). Available on

Goddard et al. (2014). The international research institute for climate and society: why, what and how. Earth Perspect, 1, 1-14.

Lee et al. (2020). Subseasonal Predictions of Tropical Cyclone Occurence and ACE  in the S2S Dataset. Weather and Forecasting, 35, 921-938.