Global warming induces an increase in global precipitation through the augmentation of evaporation. According to the IPCC, rainfall patterns are likely to be modified with some regions becoming more arid and others experiencing more rainfall.

While precipitation is increasing in eastern parts of North and South America (cf. the great USA flood of 1993), Northern Europe (severe floods in 2002 and 2005) and Northern and Central Asia, it is declining in the Sahel, the Mediterranean region, Southern Africa and in parts of Southern Asia. Drought and bushfire newly affect some regions like Australia, Pacific and Caribbean islands. The increase of precipitation aggravates flooding from the rivers in large deltas, especially in Asia, and provokes unusual inland flashfloods (Europe).

Globally the frequency of heavy precipitation has increased, drought events have intensified, have been more frequent and taken place in wider areas, especially in tropics and subtropics. For example, according to NOAA's National Climatic Data Center, precipitation in the United States of America has increased at the average rate of 6.1% since 1900 and Hawaii alone has experienced a precipitation decrease (- 9.25%). Similarly, the Australian Department of Environment and Heritage predicts for the next 30-50 years rainfall increases across the Tropical North and rainfall decreases in Southern and Eastern Australia.

Regarding cyclones there is an increase of activity in the North Atlantic since the seventies but there is no evidence, for the moment, of a global intensification of cyclone activity. However, sea level rise contributes to amplify storm surges and cyclones.

Impacts of climate change on nature and humans around the world

Again nature will have to pay a huge price for human induced climate change. Warmer temperatures and changing rainfall patterns pose a serious threat to 20 to 30% of plant and animal species. Among other dramatic cases, one can fear the progressive extinction of Amazonian rainforest and of tropical species.

Human costs of changing rainfall patterns are also heavy. For instance, China experienced catastrophic storms and floods in July 2007 as a consequence of torrential rains. These extreme weather conditions affected 20% of Chinese territory. They caused the death of more than 700 persons, and led to the evacuation of 5 millions of people. Millions of hectares of crop were destroyed. Farmers of rural areas were the most affected. In a lesser extent, coal miners were trapped in the inundated mines. Experts from the Beijing Climate Centre observe that the increase in frequency and intensity of rainstorms, droughts and heat waves in China is closely linked to global warming.

The changing in rainfall amount and patterns will have major impacts on agriculture and food security. Productivity of crops and livestock will generally decrease either because of drought and changes in soil moisture or because of floods, unusual rainfalls and soil erosion. Agriculture production is projected to decline in regions likely to be more and more affected by drought and fire like Australia, Southern Europe, Latin America or Africa. On the contrary, during the first decades of accelerated climate change some areas are likely to show yields increase for rain-fed crops.

Agriculture in industrialized countries is less likely to be vulnerable than agriculture sector in developing countries whose farmers enjoy less technological means to adapt to changing climatic conditions. However, in both cases, increased instability in agriculture production may lead to drastic increase in production cost and investment need.

Water security problems may be intensified by the growing demand of drinking water linked to world population augmentation and modern water consumption patterns. One expects a growing pressure on water resources to meet the demand for direct human consumption, agriculture, livestock, industry, energy production and natural environment.

The problems related to food and water may lead to health problems through malnutrition, hunger, famine or bacterial diseases. Increases in droughts and/or floods could affect human health through different processes.

In dried regions lack and poor quality of water associated to weak sanitation could compromise hygiene and accentuate the already deficient access to water (4/10 of the world population faces water scarcity). Cases of diarrhea, which is propagated through unsafe water and food and which already causes about 1.8 million deaths each year, are projected to increase.

Countries with poor health systems will prove to be more vulnerable to the consequences of changing rainfall, be it droughts or floods. In Bangladesh, for example, cholera epidemics associated to floods are expected to multiply as well as, in Africa, outbreaks of Rift Valley Fever linked to more frequent rainfalls. In Europe and Northern America increasing heat waves will have a negative impact on mortality, mostly affecting fragile persons (children and elderly).

Climate change and the increased incidence of vector borne diseases