Climate Exchange

[

] 77

ater

days), taking advantage of the ECMWF products, is

operational for flood and low-flow forecast for the

main French rivers, and products are delivered to the

relevant users. Seasonal forecasting is currently under

evaluation: although the signal over Western Europe

is rather dim both in terms of temperature or precipi-

tation, it has been shown that predictability can be

found for water resources, mainly due to snowpacks

in the mountain areas, delayed aquifer response and,

in very few cases, soil moisture.

No doubt in the near

future, the set of timescales offered to users will also

encompass the seasonal ones.

The information is produced on an 8 km regular

grid covering the entire territory. This makes the

management of data and the elaboration of prod-

ucts easier. Products can therefore be elaborated for

a given region or a department. Administrative divi-

sions can be chosen, and of course river basins. In this

way, the drought in the Languedoc-Roussillon admin-

istrative region in March 2012 was clearly recorded

and a warning with references to past extreme events

was issued by the authorities regarding the need for

careful usage of water. Rainy conditions during spring

brought the Soil Wetness Index (SWI) back closer

to normal, permitting a looser watch on the condi-

tions which were manageable until summer when the

drought came.

The hydrometeorological and climatical informa-

tion is delivered to actors by various means. Dedicated

websites are the main way for delivering all relevant

materials to users, both at the national level (Ministry)

and for regional and local entities. Notifications and

bulletins are produced on a monthly basis, or in case

of a particular need. Météo-France experts also take

part in hydrological coordination commissions, where

all stakeholders share their views on water use. Results

are disseminated through a website.

The agencies in

charge of water management are also directly connected

to Météo-France climatologists hotline, enabling effi-

cient support especially in case of a tricky situation.

They also collect products and data for fulfilling their

everyday duties as well as for running research and

development projects.

Climate change impact on water resources

France is concerned by the impacts of climate change

on water resources. Until recent years, attention has

been mainly paid to precipitations or river flows,

especially for large basin rivers.

In 2007, it was

decided to conduct a project tackling the effects of

climate change on water resource and droughts. The

ClimSec project had a twofold objective: to charac-

terize past evolution and to provide scenarios for the

future. It was decided to use a physical model, able to

describe the atmosphere – vegetation – soil interac-

tions rather than older parametric approaches based

on potential evapotranspiration. Quite logically, the

SIM was selected, because of its consistency with the

other productions.

gather a greater number of observations, rerun at the end of each

month so that its analysis benefits from the integration of the non-

automatic observations made by voluntary observers, and rerun

at the end of each year to retain the best homogenous archive for

climatological applications.

Project after project, day after day, the numerical suite has

been improved to represent increasingly sophisticated details

and physical processes. Research is of course still ongoing to

improve the models! A transfer of the system to the operational

teams was done in the early 2000s. Since then, it is operated

routinely, run every day in order to describe the past weather

conditions that prevailed over the country. Such an opera-

tional product is quite useful for monitoring water resources

(soil moisture, river flows) and for assessing the magnitude of

extreme events, namely droughts. The SIM system is of course

used for climate monitoring and extreme events evaluation

(notably for natural disaster assessment).

Thanks to the 1958-to-present reanalysis, a climatology of the

SIM variables is available for use. Current situations can therefore

be compared to past events or climatological references. This helps

users to evaluate the level of magnitude of a given event or situation

compared to historical references.

Daily, weekly, monthly and yearly products are used for climate

monitoring and support of the French authorities and agen-

cies in charge of water management, from national (SCHAPI,

Service Central d’Hydrométéorologie et d’Appui à la Prévision des

Inondations) to local levels. The information is tailored to cover

the various administrative districts mapping France, as well as the

hydrological watersheds and basins. The suite is used not only

for monitoring and analysis, but also for prediction. Two types

of predictions are run. Mid-range ensemble forecasting (up to 10

Climate change scenarios for two precipitation and soil wetness indices

(with logarithmic scale)