Daily Soil Water Balance Research Articles

Variability of soil water deficiencies for perennial forages in the Canadian prairie region

Variability in soil water deficiencies on the Canadian prairies was assessed by calculating forage aridity indices (FAI). These indices integrate climatic and soil parameters with water requirements for optimal forage growth. The model calculated a daily soil water balance by rain entering the soil until full capacity was reached, and evapotranspiration occurring at the potential rate. Supplemental water was added when the available soil water was reduced to 50% of the soil available water-holding capacity (AWC). The summation of these supplements constituted the forage aridity index for the growing season. Daily weather data from 1956–1985, derived for 250 agroecological resource areas (ARA) and 4 different AWCs were input to the model. The results were summarized in terms of fixed probability levels ranging from 5 to 95%. The 50 and 10% probability levels were mapped for the dominant AWC within each ARA. Regression equations were developed to account for local variability in AWC. The FAI during a “normal” year (50% probability) ranged from 66 to 496 mm, while during an ‘abnormally dry’ year (10% probability) it ranged from 180 to 579 mm. Within similar climatic regions, the 50% probability FAI of 100 mm AWC soils was approximately equal to what might be expected once every ten years (10% probability) on a 250 mm AWC soil. Relationships among FAIs at different AWCs and fixed probability levels were developed in order to estimate probability levels between 5 and 95%.

Climatological assessment of water harvesting technology through dug-out ponds in arid regions

The daily rainfall data of Bijapur for the period from 1930 to 1981 is studied to assess the feasibility of water harvesting through dug -out ponds. The initial and conditional probability analysis is done for receiving rainfall amounts of 10 to 30 mm per week to understand the continuity of wet spells. Daily soil water balance of deep black soils of Bijapur is studied to work out the availability of excess water for runoff collection. The study brings out the importance of thorough understanding of rainfall behaviour of arid regions- while developing water harvesting technology.