Report of Flooding and Submergence Working Group

The expectation that the warming effects of carbon dioxide (CO2) and other greenhouse gases will impose drier growing conditions in some areas has overshadowed attendant problems of flooding and submergence elsewhere, as the climate changes. Increased flooding is predicted as a result of changing patterns of rainfall and rising sea levels caused by melting ice and the thermal expansion of the warmer seas. Agriculturally important coastal plains are expected to suffer increasingly from decreased crop yields and manageability of the soil as water levels rise. In drier zones, greater reliance on irrigation will accelerate the rise in groundwater levels, leading to flooding and associated salinity. In addition, the long-term pressures on food production, resulting from a predicted doubling of the world’s population to 10 billion by 2060, and the warming and drying of southerly latitudes will force increased cropping in more northerly regions. In these regions, prolonged spring flooding together with freezing of flood water can be expected to cause problems of ice-encasement in the marginal zones. In more temperate latitudes, an increasing prevalence of storms in spring or early summer could prove especially damaging to young crop plants. Changes in the balance of species in the natural flora are anticipated since only a minority are equipped biochemically or morphologically to tolerate over-wet growing conditions. Even species well- adapted to flooding will come under increasing pressure if intervening periods of lowered water tables become shorter. Such damaging effects on estuarine species have already been recorded in the subsiding Mississippi Deltaic Plain.