H |
| Hadley cell circulation | The generalized circuit of air mass movement occurring between the equator and 30° latitude (north and south of the equator). The Hadley cell circulation is characterized by rising air masses at the equator and descending air masses at approximately 30º north and south latitude. |
| Hard water | Water in which relatively high amounts of minerals, mainly of calcium and magnesium salts, are dissolved. |
| Hardness | Water in which relatively high amounts of minerals, mainly of calcium and magnesium salts, are dissolved. |
| HDI | The Human Development Index (HDI) measures human development by combining three dimensions of development: longevity (life expectancy at birth), knowledge (adult literacy and mean years of schooling), and income (UNDP HDR 2008). |
| Heavy metals | Includes cadmium, copper, nickel, zinc, chromium, arsenic, mercury, lead; are persistent in the environment and can bio-accumulated in aquatic organisms. |
| Hepatitis | Inflammation of the liver caused by a viral infection. |
| Herbivore | An animal that consumes living plants or their parts. |
| Herero | One of the major tribal groups of the Orange-Senqu River basin. |
| Heterotroph | An organism that requires organic molecules as a source of energy and nutrients because it is unable to manufacture their own food using the sun’s energy. |
| Hibernate | A period of biological rest that some animal species use to conserve energy during winter months. |
| HIV | Human Immuno-deficiency Virus (HIV) is the retrovirus that attacks the human immune system resulting in AIDS. It is transmitted through direct contact of a mucous membrane with a bodily fluid containing HIV. This transmission can come in the form sexual contact; blood transfusion; contaminated needles; exchange between mother and infant during pregnancy, childbirth, or breastfeeding; or other exposure to one of the above bodily fluids. |
| Homo Sapiens | The modern species of humans, the species to which all living humans belong. The Latin meaning, ‘wise man’ reflects the greater endowment of the brain power compared to his predecessors. The species is defined in terms of anatomy, and the first member of the species is recognized from about 150 000 years ago. |
| Horizon | A layer of soil with physical and chemical properties distinct from layers above and below. |
| Hotspot | An area of extraordinarily high biodiversity. |
| Human development | A complex concept of development, based on the priority of human well-being, and aimed at ensuring and enlarging human choices which lead to equality of opportunities for all people in society and empowerment of people so that they participate in - and benefit from - the development process. |
| Human Development Index | A composite index developed to measure progress in Human Development (above) through three basic components of human development: longevity, knowledge and standard of living. |
| Humidity | A general term used to describe the amount of water vapor found in the atmosphere. |
| Husbandry | The agricultural practice of breeding or raising livestock. |
| Hydroelectric power generation | The conversion of the flow of water into electricity. |
| Hydrograph | Graph showing the variation in time of some hydrological data such as stage, discharge, velocity, sediment load, etc. (hydrograph is mostly used for stage or discharge) . |
| Hydrologic cycle | Refers to the cycling of water from the ocean to the land and back again, including all the pathways and processes connected with the storage and movement of water in solid, liquid, and gaseous states. |
| Hydrological drought | Occurs when the surface and ground water resources are in a below average depleted state for a prolonged period, usually in response to below average rainfall. |
| Hydrological regime | The long - term history of flow levels in a river. |
| Hydrology | (1) Science that deals with the waters above and below the land surfaces of the Earth, their occurrence, circulation and distribution, both in time and space, their biological, chemical and physical properties, their reaction with their environment, including their relation to living beings. (2) Science that deals with the processes governing the depletion and replenishment of the water resources of the land areas of the Earth, and treats the various phases of the hydrological cycle. |
| Hypertrophic | An acute concentration of nutrients. |
| Hyphae | Long, thread-like branching filament found on fungus. |
| Hyphomycetes | A class of fungi. |
