Interactive Index
Monthly climate indices transform daily data into meaningful metrics that can highlight trends in temperature extremes, heating and cooling demand, agricultural suitability, precipitation patterns, drought severity, soil erosion, wind characteristics and more. Each index is calculated on a monthly frequency, providing a valuable perspective for medium to long-term planning and risk assessment, particularly useful for quick analysis or simplification.
Below, you’ll find a detailed breakdown of the indices offered by Sustax, categorized by the primary climate variable they are derived from. For each index, we provide:
- Full Name (Acronym): The official name and common abbreviation.
- Definition: A clear explanation of what the index represents.
- Unit of Measurement (UoM): The units in which the index is expressed.
- Meaning & Interpretation: Guidance on how to understand the index and its implications.
- Primary Source Variable(s): The daily Sustax variable(s) used in its calculation.
Temperature Climate Indices
These indices provide insights into various aspects of thermal conditions, from average temperatures to metrics relevant for energy demand and agriculture.
Average Mean Temperature (AvMT)
- Definition: The average of the daily mean 2m air temperatures for a given month.
- UoM: Degrees Celsius (ºC)
- Meaning & Interpretation: Represents the typical average temperature for the month. Tracking AvMT over time shows warming or cooling trends. It’s a foundational metric for general climate assessment.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Maximum Mean Temperature (MxMT)
- Definition: The highest daily mean 2m air temperature recorded within a given month.
- UoM: Degrees Celsius (ºC)
- Meaning & Interpretation: Indicates the peak average daily warmth experienced during the month. Useful for understanding the intensity of warm periods and assessing heat stress potential.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Minimum Mean Temperature (MnMT)
- Definition: The lowest daily mean 2m air temperature recorded within a given month.
- UoM: Degrees Celsius (ºC)
- Meaning & Interpretation: Indicates the average of the minimum daily temperatures experienced during the month. Useful for understanding the intensity of cold periods and assessing cold stress potential.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Cooling Degree Days (CDD)
- Definition: A measure to estimate energy demand for cooling buildings. Calculated as the sum of degrees by which the daily average 2m air temperature exceeds a reference base temperature (in Sustax i.e.: 18.5°C) for each day in the month.
- UoM: Degree-days
- Meaning & Interpretation: Higher CDD values indicate a greater need for air conditioning and higher cooling energy consumption. Essential for energy sector planning, building design, and utility demand forecasting.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Heating Degree Days (HDD)
- Definition: A measure to estimate energy demand required for heating buildings. Calculated as the sum of degrees by which the daily average 2m air temperature falls below a specific reference base temperature (in Sustax i.e.: 16.5°C) for each day in the month.
- UoM: Degree-days
- Meaning & Interpretation: HDD quantifies how much and for how long a building typically needs to be heated. A higher HDD value indicates colder conditions and consequently, a greater demand for heating energy. This index is crucial for energy suppliers, building designers and engineers to optimize insulation and heating system capacity, policymakers assessing energy needs and efficiency measures, businesses managing energy costs for their facilities.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Growing Degree Days (GDD)
- Definition: Growing Degree Days (also known as GDU – Growing Degree Units or “heat units”) are used to estimate the growth and development of plants during the growing season. They are calculated as the accumulated sum of degrees by which the daily average temperature exceeds a specific reference base temperature (Tb). Different plants have different base temperatures below which their development is minimal. The reference base temperature in Sustax is of 5ºC, though it’s important to note that different crops may have different thresholds values for GDD.
- UoM: Degree-days
- Meaning & Interpretation: GDD provides a “heat score” for plant development. Warmer temperatures above the base temperature contribute to the accumulation of GDDs, and higher GDD accumulation generally correlates with faster plant growth and progression through phenological stages (e.g., germination, flowering, maturity). This index is crucial for farmers and agronomists to predict crop development stages and optimal timing for planting, pest control, and harvesting; for assessing the suitability of a region for specific crops and for understanding how climate change might alter growing seasons and crop viability; and for insurers assessing agricultural risk.
- Source Variable: tas (Daily Mean 2m Air Temperature)
Precipitation Climate Indices
These indices help quantify various aspects of precipitation, including dryness, total rainfall, intensity of rain events, and potential for soil erosion.
Consecutive No-rain Days (DAR30 / DAR05)
- DAR30 Definition: The maximum number of consecutive days in the month where daily accumulated precipitation is less than 3.0 mm (considered “no significant rain”). Useful for rainy areas.
- DAR05 Definition: The maximum number of consecutive days in the month where daily accumulated precipitation is less than 0.5 mm (considered “effectively no rain”). Useful for dry areas.
- UoM: Days
- Meaning & Interpretation: Indicates the length of dry spells. DAR30 is useful for generally rainy areas, while DAR05 is more relevant for drier regions where even small amounts of rain are significant. High values point to drought conditions and water stress.
- Source Variable: pr (Accumulated Total Precipitation)
Total Monthly Accumulated Rain (RT)
- Definition: The total amount of precipitation (liquid and frozen, including rain and snow) that has accumulated over all days within a given month. This is calculated by summing the daily total precipitation values for each day of the month.
- UoM: depth in meters (m)
- Meaning & Interpretation: RT provides a straightforward measure of the total rainfall/snowfall received in a month. It’s a fundamental indicator for assessing overall water availability and a region’s wetness or dryness relative to its norms; for water resource management, reservoir planning, and agricultural irrigation needs; and for understanding general hydrological conditions and long-term precipitation trends (e.g., increasing or decreasing monthly totals).
- Source Variable: pr (Accumulated Total Precipitation)
Wettest Day (RX1day)
- Definition: The highest amount of precipitation (liquid and frozen) that accumulated in a single 24-hour period (one day) within a given month.
- UoM: depth in meters (m)
- Meaning & Interpretation: RX1day indicates the magnitude of the most intense single-day rainfall or snowfall event during the month. It is a key indicator for:
- Assessing the risk of flash floods, urban flooding (when drainage capacity is exceeded), and landslides triggered by heavy downpours.
- Designing infrastructure (e.g., storm drains, culverts) to withstand extreme precipitation events.
- Understanding the potential for soil erosion caused by intense rainfall.
- Tracking changes in the intensity of extreme precipitation events over time, which is a common signal of climate change.
- Source Variable: pr (Accumulated Total Precipitation)
Monthly Average Precipitation (RA)
- Definition: The average amount of daily accumulated precipitation over all days within a given month. It is calculated by summing the daily total precipitation values for each day of the month and then dividing by the number of days in that month.
- UoM: depth in meters (m)
- Meaning & Interpretation: RA represents the typical or average daily precipitation amount for a specific month. It helps in:
- Understanding the general daily moisture input for a location during that month.
- Comparing the “average day’s rain” across different months or years.
- Agricultural planning, particularly for assessing general water availability from rainfall.
- Distinguishing between months with frequent light rain versus months with infrequent but heavy rain, especially when analyzed alongside indices like RT (Total Monthly Rain) and RX1day (Wettest Day).
- Source Variable: pr (Accumulated Total Precipitation)
Monthly Modified Fournier Index (MFI)
- Definition: The Monthly Modified Fournier Index is an indicator of potential soil erosion due to rainfall impact, often referred to as rainfall aggressiveness or erosivity. For a given month, it is calculated using the square of the average daily precipitation for that month, divided by the average daily precipitation for the entire year to which that month belongs.
- UoM: Dimensionless
- Meaning & Interpretation: MFI provides insight into how the rainfall in a particular month contributes to potential soil erosion compared to the annual average. A higher MFI value for a month suggests that the rainfall during that month was particularly aggressive (e.g., high average intensity relative to the year) and thus has a greater potential to cause soil erosion. It considers both, the monthly rainfall amounts and how they compare to the yearly average. While this is a monthly MFI, the sum of the 12 monthly MFI values (in millimetres) for a year yields the annual MFI, which can be compared against established thresholds for erosion risk (e.g., 0 – 60 very slow, 60 – 90 slow, 90 – 120 moderate, 120 – 160 high or >160 very high) [13]. This index is particularly relevant for agriculture, land management, conservation planning, and infrastructure projects in areas prone to erosion.
- Source Variable: pr (Accumulated Total Precipitation)
Rain over 95th/99th Percentile (R95tot / R99tot)
- Definition (R95tot): The percentage of total monthly precipitation that came from days where daily precipitation exceeded the 95th percentile of daily precipitation values (calculated over the whole climate model’s time series as a reference period).
- Definition (R99tot): Similar to R95tot, but for days exceeding the 99th percentile.
- UoM: Percentage (%)
- Meaning & Interpretation: Indicates the contribution of very heavy (R95tot) or extreme (R99tot) rainfall events to the total monthly precipitation. High values suggest that a large portion of the rain falls in intense bursts, which can increase flood risk and soil erosion.
- Source Variable: pr (Accumulated Total Precipitation)
Wind Gusts Climate Indices
These indices provide insights into the characteristics of wind speed, particularly focusing on maximum gusts and the frequency of extreme wind events. This information is vital for assessing structural risks, planning for operational disruptions in wind-sensitive industries, and understanding renewable energy potential. All Sustax wind indices are derived from the daily Maximum Wind Gust (sfcWindmax) data.
Maximum Wind Gust (fxx)
- Definition: The highest daily maximum wind gust (sfcWindmax) recorded at 10 meters above the surface during any day within a given month.
- UoM: Meters per second (m/s)
- Meaning & Interpretation: fxx represents the absolute peak wind gust intensity experienced during the month. It is a critical indicator for:
- Assessing the most extreme wind conditions a structure or asset might face.
- Designing infrastructure to withstand peak wind loads.
- Understanding the potential for significant, acute wind-related damage.
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)
Minimum Wind Gust (fmx)
- Definition: The lowest daily maximum wind gust (sfcWindmax) recorded at 10 meters above the surface during any day within a given month.
- UoM: Meters per second (m/s)
- Meaning & Interpretation: fmx indicates the peak wind gust on the “calmest” day of the month (in terms of daily peak gusts). While less commonly used for extreme risk assessment than fxx, it can provide context on the lower bound of daily peak wind activity or the prevalence of days with very low peak gusts. For example, consistently low fmx values might be relevant for periods requiring calm conditions (e.g., certain construction activities, drone operations).
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)
Extreme Wind Days (xf98)
- Definition: The number of days in a given month where the daily maximum wind gust (sfcWindmax) exceeded the 98th percentile. This percentile is typically calculated based on the distribution of daily maximum wind gusts over a long-term historical reference period (e.g., 1979-2022) for that specific location and time of year.
- UoM: Days
- Meaning & Interpretation: xf98 quantifies the frequency of days with exceptionally strong wind gusts relative to the local climatology. An increase in xf98 suggests more frequent occurrences of potentially damaging wind events. This is important for:
- Forestry (risk of windthrow).
- Agriculture (crop damage).
- Building and infrastructure design and insurance risk assessment.
- Offshore and onshore energy operations.
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)
Consecutive Extreme Wind Days (xf98C)
- Definition: The longest continuous sequence of days within a given month where the daily maximum wind gust (sfcWindmax) exceeded the 98th percentile (calculated as per xf98).
- UoM: Consecutive Days
- Meaning & Interpretation: xf98C highlights the persistence of extremely windy conditions. Prolonged periods of high wind gusts can exacerbate damage, increase stress on structures, and lead to extended operational disruptions. This index provides a more nuanced view of extreme wind risk than just the count of individual extreme wind days (xf98).
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)
Days with Wind Gusts above 21 m/s (dfx21)
- Definition: The number of days in a given month where the daily maximum wind gust (sfcWindmax) was equal to or greater than 21 meters per second (approximately 75.6 km/h or 47 mph). This threshold corresponds to a strong gale on the Beaufort scale, capable of causing structural damage.
- UoM: Days
- Meaning & Interpretation: dfx21 provides a count of days experiencing significantly strong, potentially damaging wind gusts based on an absolute threshold. It’s a practical measure for:
- Operational planning where activities are suspended above certain wind speeds.
- Assessing the frequency of conditions that could lead to damage to infrastructure, power outages, or transportation disruptions.
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)
Consecutive Days with Wind Gusts above 21 m/s (dfx21C)
- Definition: The longest continuous sequence of days within a given month where the daily maximum wind gust (sfcWindmax) was equal to or greater than 21 m/s.
- UoM: Consecutive Days
- Meaning & Interpretation: dfx21C measures the persistence of strong gale-force wind gusts. Extended periods of such conditions can significantly increase the risk of widespread damage and prolonged disruptions to services and operations.
- Source Variable: sfcWindmax (Daily Maximum Wind Gust)