Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Tuesday 7 July - 16:30-18:00 UNESCO Fontenoy - ROOM XII

1119 (a) - Extreme hydrological events: Deciphering changes in hazard and risk at different time-scales

Parallel Session

Lead Convener(s): H. Kreibich (German Research Centre for Geosciences, Potsdam, Germany)

Convener(s): G. Mahe (Institut de Recherche pour le Développement, Montpellier cedex 5, France), J.M. Martinez (IRD, Toulouse, France), J.E. Paturel (IRD, Abdijan, Ivory Coast), B. Turcq (Institut de Recherche pour le Développement, Lima, Peru)

16:30

Review of Hydrological norms for Climate Change Resilient Hydraulic Infrastructures in Africa (RESIHYST-Africa): towards a regional programme

A. Amani (UNESCO, Nairobi, Kenya)

Abstract details
Review of Hydrological norms for Climate Change Resilient Hydraulic Infrastructures in Africa (RESIHYST-Africa): towards a regional programme

A. Amani (1)
(1) UNESCO, Hydrololgic international programme, Nairobi, Kenya

Abstract content

In order to address the current and future water needs and to boost the economic growth of African countries, it is crucial to improve substantially the current rate of mobilization of renewable water resources which is less than 5%. Hydraulic infrastructures (Dams) with various sizes are needed to increase substantially the level of water storage. For road construction, urban water drainage and flood protection other types of hydraulic infrastructures are needed. In many African countries, guidelines and hydrological norms currently used by engineers and managers are obsolete.

 

In West Africa for example, particularly francophone countries, the hydrological norms for the design of hydraulic infrastructures currently used were established during 60-70s. These norms were established based on hydrological data collected from around 200 experimental basins in West and Central African countries for a period of 3 to 5 years during and following the International Hydrological Decade which led to the creation of the UNESCO International Hydrological Porgramme. In regard to the ecological and climate changes recorded within the region and the huge consequence on infrastructures safety and with the future climate change, there is an urgent need to review and adapt these norms for a resilient design of hydraulic infrastructures in the region.  Within the framework of its International Hydrological Programme and on the request of countries through a resolution of IHP Africa national committees UNESCO has initiated a regional programme to address the issue of hydrological norms for the design of hydraulic infrastructures within the context of climate change with a focus for the first phase on West and Central Africa. The first phase of the programme will concern 26 countries from ECOWAS and ECCAS. Two experts working meetings have been held in Ouagadougou. Twelve baseline studies have been conducted in the following countries: Senegal, Niger, Ivory Coast, Guinea, Togo, Benin, Chad, Cameroon, Congo, CAR, DRC and Rwanda.  

 

The regional programme will have the following components: i) Data and hydrological monitoring: new basins should be monitored in partnership with hydrological services and universities and all available climate and hydrological data capitalized; ii) Analysis, Methods and Modelling: Based on the available and collected new data, hydrological research will be conducted focusing on techniques, methods and hydrological modelling for a robust and adapted assessment of discharges taking into account non the stationarity; iii) Operational tools: proposition of new adapted hydrological tools (guidelines, softwares,..) and iv) Capacity building and promotion of the new tools: capacity building at various levels including technician, engineer, graduate and a wide dissemination of the new tools will be considered.

There is an urgent need to mobilze key stakeholders and donors for the funding of the programme which has been endorsed by  ECCAS and ECOWAS.

16:55

Extreme seasonal hydrological events in the Amazon Basin

J. C. Espinoza (Peruvian Geophysical Institute IGP, Lima, Peru), J. Ronchail (LOCEAN and Université Paris Diderot, Paris, France), N. Filizola (Federal University of Amazonas, Manaus, Brazil), P. Fraizy (IRD (Brazil), Manaus, Brazil), J.-L. Guyot (IRD, Lima, Peru), J. M. Martinez (IRD, Toulouse, France), L. Noriega (Servicio Nacional de Meteorología e Hidrología, La Paz, Bolivia), W. Santini (IRD, Lima, Peru), F. Timouk (IRD, La Paz, Bolivia)

Abstract details
Extreme seasonal hydrological events in the Amazon Basin

JC. Espinoza (1) ; J. Ronchail (2) ; N. Filizola (3) ; P. Fraizy (4) ; JL. Guyot (5) ; JM. Martinez (6) ; L. Noriega (7) ; W. Santini (5) ; F. Timouk (8)
(1) Peruvian Geophysical Institute IGP, SCAH, Lima, Peru; (2) LOCEAN and Université Paris Diderot, Paris, France; (3) Federal University of Amazonas, Manaus, Brazil; (4) IRD (Brazil), Manaus, Brazil; (5) IRD, Lima, Peru; (6) IRD, GET Laboratory, Toulouse, France; (7) Servicio Nacional de Meteorología e Hidrología, La Paz, Bolivia; (8) IRD, La Paz, Bolivia

Abstract content

The Amazon basin is the world’s major hydrologicalsystem. Its watershed covers about 6,000,000 km2, almost 5% of all continental masses, andits average discharge is the greatest inthe world (±200,000m3/s). During the last decades, an intensification of extreme seasonal hydrological events (droughts and floods) has been reported in the Amazon region, producing strong impacts on humans and natural systems. In this contribution we propose a synthesis of the key aspects of the recent extremes droughts and floods in the Amazon basin from the Andean regions to the lowland rainforest, including their causes and main impacts. Our results are based on large-scale climate data and observed hydrological information coming from the whole Amazonian countries, in the context of the SO-HYBAM observatory. A trend towards an intensification of the hydrological cycle has been reported during the last decades. For instance, in the Peruvian Amazon, a significant discharge diminution trend (p<0.01) is noticed during the low-water season; indeed discharge decreased by 30% after the 1990s when comparing to the 1970-1989 period. However, no trend is observed during the high-water season but extreme floods have recently occurred (e.g. 1999, 2012). Extreme hydrological events have been frequently related to sea surface anomalies in the Pacific and Atlantic oceans. For instance, intense rainfall and subsequent floods have been associated with La Niña events (e.g. 1989, 1999, 2011 and 2012) or to warm conditions in the tropical South Atlantic, as observed in 2009. However the 2014 rainfall and flood anomalies have been related to warm conditions in the western Pacific-Indian Ocean and to exceptional positive anomalies in the Subtropical South Atlantic. Rainfall deficits and droughts have been attributed to El Niño events (e.g. 1998), or to warm conditions in the tropical north Atlantic (e.g. 2005) or to a combination of both oceanic features (e.g. 2010).

17:20

Evolution rain-vegetation-agricultural yields in the watershed of the Bouregreg (Morocco) from 1980 to 2009

Z. A. Tra Bi (Alassane Ouattara University, Bouaké, Ivory Coast), G. Mahe (Institut de Recherche pour le Développement, Montpellier cedex 5, France), T. Brou, (UMR 228 ESPACE-DEV (IRD, UM2, UAG, UR), Saint Denis, France)

Abstract details
Evolution rain-vegetation-agricultural yields in the watershed of the Bouregreg (Morocco) from 1980 to 2009

ZA. Tra Bi (1) ; G. Mahe (2) ; T. Brou, (3)
(1) Alassane Ouattara University, Geography Department, Bouaké, Ivory Coast; (2) Institut de Recherche pour le Développement, Milieu et Environnement, Montpellier cedex 5, France; (3) UMR 228 ESPACE-DEV (IRD, UM2, UAG, UR), Saint Denis, France

Abstract content

Bouregreg Watershed (central Northwest of Morocco) belongs to the agricultural area of Morocco. The agricultural area of the country is only 20% of its national territory, where a strong agricultural and pastoral attractiveness for wet areas like Bouregreg watershed. This watershed is subject to a Mediterranean semiarid climate. Precipitations that fall are estimated, on average, 400 mm per year. They are unevenly distributed over the basin. Thus, the altitude is causing a significant rainfall contrast between Northeast parts of the basin where rainfall rising to 760 mm per year and Southwest areas where they drop to less than 350 mm per year. In addition, climate dynamics of this space, since the 1970s, is marked by strong climate variability with a downward trend in rainfall. This is a major concern for the agricultural and pastoral production; especially that agriculture is mainly rainfed. The crop production system (natural or cultivated) is heavily influenced by the soil and climate conditions in Bouregreg watershed.

This study analyzes the interaction between changes in precipitation and dynamics of crop production from 1980 to 2009. It is a component of the SIGMED (project Spatial approach to the impact of agricultural activities in the Maghreb on sediment transport and water resources in large river basins). The study focuses on the impact of droughts and wet periods on crop production. To achieve this goal, a time series of comparative statistical analysis is first performed on Normalized Difference Vegetation Index (NDVI) of NOAA (National Oceanic and Atmospheric Administration) and MODIS (Moderate Resolution Imaging Spectroradiometer), made in space mesh of 8 km x 8 km, and rainfall series. In holding the large spatial variations in rainfall in the basin, the analysis is made by homogeneous climatic unit. Then, a special statistical analysis is performed on the dynamics of agricultural production, frequencies and intensities of agricultural drought. Droughts and their intensity are determined by linear regression of cereal production with a 95% confidence interval.

The analysis of the evolution of vegetation reveals significant interannual variation in plant activity (37% coefficient of variation), with a marked tendency to decline in the summer. A break in the dynamics of plant activity of the basin is observed in 1999: Reductions are 13% and plant activity maxima are before 1995. The largest areas are located downstream, in the center and south of the basin. The analysis of changes in rainfall also highlights an interannual variation of 30 to 40%, with deviations from the average, greater than 120 mm. Paradoxically, there is no annual downward trend in rainfall amounts in downstream, the center and the south of the basin, but in the northeast that is the wettest area of the basin. In addition, the observation of a significant decrease of vegetation in the summer is not correlated to changes in rainfall. For cons, the correlation between precipitation and vegetation change in wet period (growing season) is important. The analysis of the evolution of wheat (soft and hard) and barley agricultural droughts (the three grains representing ¾ of agricultural production of the basin) allows to notice a declining intra seasonal dynamic of rainfall amounts during wet periods. Agricultural drought is particularly great between 1990 and 2002. Analysis of drought frequency for all three cereals allows concluding that the period from 1980 to 2009 was marked by eleven important agricultural droughts. The intensities of droughts between 1990 and 2002 are between 60 and 80% for these cereals. Thus, the high productions of certain grains such as wheat are mainly related to the conquests of new lands. Yield reductions are offset by an extension of cultivation areas at the expense of forests and fallow land. In addition, the overall decline in plant activity in summer is related to increasing grazing pressure and thus to a rapid depletion of crop residues. This further leads to another pressure on forest vegetation and scrub.

17:33

Monitoring and seasonal forecasting of droughts in China

X. Yuan (Institute of Atmospheric Physics, Chinese Academy of Sciences and Princeton University, Beijing, China)

Abstract details
Monitoring and seasonal forecasting of droughts in China

X. Yuan (1)
(1) Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Abstract content

Persistent hydrologic extreme events such as droughts have devastating impacts on the human and natural systems. Their occurrences are associated with anomalous atmospheric moisture transport which may be linked to variations of large-scale climate phenomena (e.g., ENSO), and their severities and durations are also influenced by land-atmosphere coupling that can enhance existing extremes. They may be further exacerbated by anthropogenic climate change and human water consumption. Improving our monitoring and forecasting capability of droughts, and facilitating adaptations through establishing climate service systems at regional to global scales, are among the grand challenges proposed by the WCRP, and are the core themes of the GEWEX/RHP. Focusing on the major river basins in China, I will show the quality of the latest satellite surface soil moisture retrievals produced by the European Space Agency Climate Change Initiative (ESA CCI) for drought monitoring, and the drought predictability and forecast skill based on North American Multi-Model Ensemble (NMME) climate forecast models.

As compared with in-situ observations at 312 stations in China and global reanalysis, the ESA CCI soil moisture products provide independent drought information over sparsely observed regions such as northwestern China, and the active microwave product with better vegetation penetration works the best in southern China. Although remote sensing products can only detect less than 60% of drought months over most in-situ stations, they capture the responses of inter-annual drought variations to ENSO at river basin scales quite well.

For drought forecasting using NMME models, the drought predictability is quantified by using a perfect model assumption. Drought predictability and forecast skill are positively correlated, but they vary depending on seasons, regions and forecast leads. Higher drought predictability is found over regimes where ENSO has more significant impact. For the ENSO-affected regimes, both drought predictability and forecast skill in ENSO years are higher than that in neutral years.

The outputs from NMME climate forecast models are bias corrected and downscaled to drive a hydrologic model to produce hydrologic drought (in terms of soil moisture or runoff anomaly) forecasts over river basins in China. Hydrologic hindcasts will be performed and evaluated against in-situ station observations and satellite products for a comprehensive analysis.

17:46

Trends in Precipitation Extremes over Mississippi and Yangtze River Basins in CMIP5 Models

Z. Pan (Saint Louis University, St. Louis, Missouri, United States of America)

Abstract details
Trends in Precipitation Extremes over Mississippi and Yangtze River Basins in CMIP5 Models

Z. Pan (1)
(1) Saint Louis University, Earth and Atmospheric Sciences, St. Louis, Missouri, United States of America

Abstract content

Both central-eastern portions of U.S. and China are prone to increasing flooding from Mississippi River and Yangtze River Basin respectively. This presentation contrasts historical and projected spatial-temporal distribution of extreme precipitation in these two large river basins using 31 CMIP5 models’ historical and RCP8.5 experiments.  Results show that 1) over both river basins, the heaviest rainfall events have increased in recent decades while the lightest precipitation reduced in frequency.  Over Mississippi River Basin, both the lightest precipitation (<2.5 mm/day) and heaviest (>50 mm/day) would decrease in frequency notably after mid-2020s while intermediate events occur more frequently in future; whereas over the Yangtze River Basin, all categories of precipitation are projected to increase in frequency over the coming decades. 2) Although the consensus of CMIP5 models was able to reproduce well domain-time mean and even time-averaged spatial distribution of precipitation, they failed to simulate precipitation trends both in spatial distribution and time means. In a similar fashion, models captured well statistics of precipitation but they had difficulty in representing temporal variations of different precipitation intensity categories.  3) The well-documented 2nd half of the 20th century surface summer cooling over the two river basins showed different associations with precipitation trends with higher anti-correlation between them over the U.S. region, implying different processes contributing to the cooling mechanisms of the two river basins.