Hazards definitions

This page provides a general definition of each climate hazard, and the corresponding categories used to define categories of no significant stress, moderate, severe, and extreme.

Hazard	Indicator (units)	Description	Categories	Acronym
Heat stress	Heat stress humans basic	Used in Phase 1. The heat index (HI) was calculated from daily data and empirical equations based on Steadman (1979a; 1979b) relating the HI to dry-bulb temperature (°C) and relative humidity (%). The equation is as follows, HI = c1 + c2 * T + c3 * R + c4 * T * R + c5 * T^2 + c6 * R^2 + c7 * T^2 * R + c8 * T * R^2 + c9 * T^2 * R^2 T is the dry bulb temperature in ºC (taken to be the daily mean temperature). R is the relative humidity in %, and the values of the constants c1 to c9 are: c1=-8.78469475556; c2=1.61139411; c3=2.33854883889; c4=-0.14611605; c5=-0.012308094; c6=-0.0164248277778; c7=2.211732 x 10^-3; c8=7.2546 x 10^-4; c9=-3.582 x 10^-6. Using the daily values we can calculate: (1) the annual mean HI; (2) the monthly mean, and then the maximum of all months; and (3) the frequencies (probabilities) of each HI category. References * Steadman RG. 1979a. The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science. Journal of Applied Meteorology. 18 (7): 861–873. * Steadman RG. 1979b. The Assessment of Sultriness. Part II: Effects of Wind, Extra Radiation and Barometric Pressure on Apparent Temperature. Journal of Applied Meteorology. 18 (7): 874–885. * See wikipedia page at https://en.wikipedia.org/wiki/Heat_index	Mild or no stress: < 27 Caution: 27–32 Extreme caution: 32-41 Danger & Extreme danger: > 41 (with extreme danger being > 54)	HSH
Heat stress	Heat stress humans (ºC)	Equal to the wet bulb temperature (in ºC), which is calculated as Tw=T * atan[0.151977 * (RH% + 8.313659)^0.5] + atan(T + RH%) - atan(RH% - 1.676331) + 0.00391838 * (RH%)^(3/2) * atan(0.023101 * RH%) - 4.686035. Taken from Stull (2011). T is the air temperature (in ºC), and RH is the relative humidity (in %). From this, various indicators can be calculated, including: (1) the seasonal, annual, and multi-year frequencies (probabilities) of each category; (2) the average wet bulb temperature of a month; and (3) the average across months and the maximum across months. For (3) one would use the monthly, not daily, values.	Mild or no stress: < 25 Caution: 25–30 Danger: 30-35 Extreme danger: > 35	HSH_TW
Heat stress	Heat stress humans new	To be added. Based on new work being done by Jerry Nelson and Philip Thornton (not yet published)
Heat stress	Heat stress livestock (cattle) (THI units)	The daily thermal humidity index (THI) is calculated following Rahimi et al. (2020), as THI1 = (1.8 × Tdb + 32) − [(0.55 – 0.0055 × RH) × (1.8 × Tdb − 26.8)]. Tdb is the dry bulb temperature (assumed to be the maximum temperature, ºC), and RH is the relative humidity (%). The THI values are then classified. Each of these categories is given an integer value. Finally, various indicators can be calculated, including: (1) the seasonal, annual, and multi-year frequencies (probabilities) of each category; (2) the average THI of a month; and (3) the average across months and the maximum across months. For (3) one would use the monthly, not daily, values.	No stress: ≤ 72 Mild stress: 73–78 Moderate stress: 79–89 Severe stress: ≥90	THI
Heat stress	Heat stress livestock (multiple species) (THI units)	The daily thermal humidity index (THI) can be be calculated following Thornton et al. (2021), using the same equation as above, but instead of using the maximum temperature, using the daily mean temperature (ºC). The THI values are then classified into two categories: (1) extreme heat stress; and (2) no extreme heat stress. Finally, various indicators can be calculated, including: (1) the annual, and multi-year frequencies (probabilities) of extreme heat stress; (2) the average THI of each month; and (3) the annual average (mean of all days) and the maximum across months (max of all months). Thornton et al. (2021) proposed thresholds for several livestock species, which we use here. We use thresholds for "tropical" areas, per Table 2 of Thornton et al. (2021)	Cattle: 94 Goats: 94 Sheep: 93 Pigs: 92 Poultry: 92	THIMS
Heat stress	Extreme heat stress for crops (days), Tmax > 40ºC	The number of days with daily maximum temperatures above a given threshold. We compute this for each month of the year, using a temperature threshold of 40ºC, and no crop calendar (i.e., we calculate it for the whole year).	No significant stress: 0 Moderate: 1 – 5 Severe: 5 – 10 Extreme: > 10	NTx40
Heat stress	Heat stress for crops (days), Tmax > 35ºC	The number of days with daily maximum temperatures above a given threshold. To compute this, we use a temperature threshold of 35ºC, and no crop calendar (i.e., we calculate it for the whole year).	No significant stress: < 10 Moderate: 10 – 20 Severe: 20 – 25 Extreme: > 25	NTx35
Heat stress	Heat stress maize	The number of days with daily maximum temperatures above a given threshold during the flowering period. To compute this, we use a maize crop calendar (and focus on the main rainy season), and assume the flowering period occurs in the middle month of the season. Cropping calendars are taken from Sacks et al. (2010). For maize, we use a temperature threshold of 35ºC (note, it is Tmax), and assume that at this temperature heat stress starts affecting maize plants.	No significant stress: < 10 Moderate: 10 – 20 Severe: 20 – 25 Extreme: > 25	HSM
Drought stress	Thornthwaite's Aridity Index (%)	Thornwaite aridity index = 100 * (d / n), where d = sum of monthly differences between prec and PET for months where precip < PET, and n = sum of monthly PET for those months. Note this index is calculated using the ENVIREM R package directly. ENVIREM takes a global solar radiation estimate (available here) to compute PET, and then uses that and precipitation to compute the Thornthwaite Aridity Index. Phase 1 script available here.	No significant stress: <40 Moderate stress: 40–60 Severe: 60–80 Extreme: >80	TAI
Drought stress	Number of dry days (days)	Number of dry days (P < 1 mm) per month and per year for period 1995–2014 (yearly and long-term mean), calculated using CHIRPS data.	No significant stress: < 15 Moderate: 15 to 20 Severe: 20 to 25 Extreme: > 25	NDD
Drought stress	Number of soil water stress days (days)	Number of water stress days. A water stress day is a day in which the actual to potential evapotranspiration ratio (Ea/Ep) is < 0.5. Ea/Ep is computed using a simple water balance model that uses daily CHIRPS, CHIRTS data, generated solar radiation, and soil water holding capacity data. Soils data from SoilGrids 1km. Solar radiation is from ERA5.	No significant stress: < 15 Moderate: 15 to 20 Severe: 20 to 25 Extreme: > 25	NDWS
Waterlogging & flodding stress	Number of waterlogging days (days) at 50% saturation	Number of days with soil logged by water. A waterlogging day is a day in which the soil moisture is above field capacity and moving toward saturation. Soil moisture calculated using a simple watbal routine as for the number of water stress days. Met input from CHIRPS (precipitation), CHIRTS (temperatures), ERA5 (solar radiation), and soils data from SoilGrids 1km. We use 50% of the way to saturation (i.e., half-saturated soil).	No significant stress: < 2 Moderate: 2 to 5 Severe: 5 to 8 Extreme: > 8	NDWL50
Waterlogging & flodding stress	Number of waterlogging days (days) at start of saturation	Number of days with soil logged by water. A waterlogging day is a day in which the soil moisture is above field capacity and moving toward saturation. Soil moisture calculated using a simple watbal routine as for the number of water stress days. Met input from CHIRPS (precipitation), CHIRTS (temperatures), ERA5 (solar radiation), and soils data from SoilGrids 1km. We use 0% of the way to saturation (i.e., at the very start).	No significant stress: < 2 Moderate: 2 to 5 Severe: 5 to 8 Extreme: > 8	NDWL0