Roland Schulze

Transcending scales of space and time in impact studies of climate and climate change on agrohydrological responses

Abstract The scale “jump” in hydrology and agriculture from the small scale at which individual processes such as infiltration, soil water redistribution, evapotranspiration, soil loss or crop development/yield have been studied, to the global scale at which climate change impacts and international trade in agriculture manifest themselves, has presented agrohydrologists with conceptual as well as practical problems of scales and scaling. In this context, selected scaling issues are, therefore, identified and highlighted. The paper discusses why scaling problems arise, defines concepts and types of scales, poses what are considered key questions with regard to upscaling and downscaling, as well as to dis-aggregation to homogenous landscape response units (HLRUs) and to re-aggregation. Examples from southern Africa are then given of space/time scaling approaches, ranging from country to local-scale levels, followed by an evaluation of types of errors associated with scaling. The paper concludes by identifying what, in the author’s perception, some of the challenges are which relate to scaling applications of the “real world” and which hydrologists and agriculturists face in the next few years.

Global climate change and agricultural productivity in southern Africa

Abstract An analysis tool was developed to simulate primary productivity and crop yields for both present and possible future climate conditions. Southern Africa was delineated into 712 relatively homogeneous climate zones, each with specific climate, soil and vegetation response information. The primary productivity and crop yield models were linked with the climate zones via a cellbased agrohydrologlcal model, with the final output coordinated using a Geographic Information System. The results of this preliminary study show a large dependence of production and crop yield on the intra-seasonal and inter-annual variation of rainfall. The most Important conclusion from the study is the readiness of the developed tool and associated infrastructure for future analysis into social, technological and political responses to food security in southern Africa.

Coping with variability and change: Floods and droughts

Floods and droughts are natural phenomena for which the risks of occurrence are likely to continue to grow. Increasing levels of exposure and insufficient adaptive capacity are among the factors responsible for the rising vulnerability. The former is conditioned by anthropopressure (e.g., economic development of flood-prone areas) and adverse effects of climate change; scenarios for future climates indicate the possibility of amplified water-related extremes. This article presents the current situation of coping with extreme hydrological events within the pressure-state-response framework. Among promising response strategies, the role of forecast and warning, and of watershed management are reviewed. Sample success stories and lessons learnt related to hydrological extremes are given and policy implications discussed.

Global Climate Change and Agricultural Productivity in Southern Africa: Thought for Food and Food for Thought

The population of southern Africa (defined in the context of this paper as the Republic of South Africa, plus the Kingdoms of Lesotho and Swaziland) is projected to increase from its present 40 million to between 70 and 90 million by the year 2035. To meet the food demands of this growing population, crop production will have to expand at three per cent per annum (Arbuthnot, 1992). This will not be an easy task, however, as the southern African subcontinent is largely semi-arid and sub-humid, has a diversity of soils, physiography, agricultural crops grown, and management levels at which they are grown. Above all these factors, however, is the wide range of climates, characterised by a marked intra-seasonal and inter-annual variability of rainfall. In terms of resource management, this is a high-risk environment which, in the agricultural industry, be it in the commercial or subsistence sector, implies in most areas uncertain production, frequent crop failures and consequently a drain on state finances through subsidies and drought relief.

U.N. hydrology initiative pairs societal needs with science

In many developing countries, human suffering due to water-related issues is on the rise. At times, the paradox of droughts and floods occurring simultaneously in neighboring regions, or consecutively within the same region, is responsible. There are persistent problems of water scarcity for basic health, frequent and deadly flooding, extensive pollution of drinking water and of waters where fish are caught. Moreover, forecasts are predicting greater water shortages, as well as excesses and degradations for many regions [Johnson et al., 2001].