Manual for describing land degradation indicators

Table of Contents

1. Editor
2. Introduction
3. Classification of indicators
4. Land degradation indicators
5. Evaluation and short-list of indicators
6. Explanations for filling the information sheets
   1. General information
   2. Climate indicators
   3. Water indicators
   4. Soil indicators
   5. Vegetation indicators
   6. Water runoff indicators
   7. Forest fires indicators
   8. Agricultural indicators
   9. Cultivation indicators
   10. Husbandry indicators
   11. Land management indicators
   12. Land use indicators
   13. Water use indicators
   14. Tourism indicators
   15. Social indicators
   16. Institutional indicators
7. Farm survey research
8. Focus group approach
9. References

Climate indicators

Climate is an important factor affecting plant growth, water availability, water demands, and land degradation. The uneven annual and inter-annual distribution of rainfall, the occurrence of extreme events, and the lack of rain water during the growing period of plants in the semi-arid and arid zones is the main climatic factor that contribute to the increasing water demands and degradation of land. The atmospheric conditions that create large water deficits which are used as indicators for assessing land degradation and desertification are: air temperature, rainfall, aridity index, potential evapotranspiration (ETo), rainfall seasonality, and rainfall erosivity.

Air temperature: yearly average air temperature (in ^oC) is collected from meteo stations located into or nearby the hot spot areas.

Rainfall: yearly average rainfall (in mm) is collected from meteo stations located into or nearby the hot spot areas.

Aridity index: can be defined as the ratio between mean annual precipitation (P) and mean annual evapotranspiration (ETo). It is a critical environmental factor affecting the evolution of natural vegetation and therefore rain erosivity by considering rainfall and air temperature. The aridity index can be also estimated by the Bagnouls-Gaussen index (BGI) using the following equation:

Where: ti is the mean air temperature for month i in 0°C, Pi is the total precipitation for month i in mm; and k represents the proportion of month during which 2ti - Pi >0.

Potential evapotranspiration: There are several methods for calculating ETo from meteorological data. The simplest method uses the average air temperature. The most complex methods require hourly data such as solar radiation, air temperature, wind speed, and the vapour pressure. The Penman-Monteith method as modified by Allen (1986) can be used for the purposes of this project.

Rainfall seasonality: is related to the temporal distribution of rainfall (monthly). There are three possible ways of calculation:

• Season rainfall/total rainfall (%)
• Monthly rainfall/total rainfall (%)
• Seasonality Index (SI) (derived by Walsh and Lawler (1981) for determination of the months with most rainfall seasonality

The season rainfall/total rainfall (%) index takes values from 0 to 100%. The statistical theoretic "normal" value for each season is 25%. The monthly rainfall/total rainfall (%) index has an equal distribution approximately 8% per each month. The bigger the difference from this value, the highest the rain seasonality. The following equation is used for calculating the seasonality Index (SI) according to Walsh and Lawler (1981):

Where Ri is the total annual precipitation for the particular year under study and Xin is the actual monthly precipitation for month n. The rainfall seasonality can be assessed by using the following SIi index.

Rainfall erosivity: Rainfall erosivity depends primarily on rainfall intensity and amount. For calculating erosivity: a modified version of the Fournier index (FI) is used as follows:

Where Pi is the precipitation total in month i, and p is the mean annual precipitation total. The Fournier index is then classified as follows: