Climate Variability

Climate variability refers to variations in the mean state and other statistics (such as standard deviations, the occurrence of extremes, etc.) of the climate on all spatial and temporal scales beyond that of individual weather events.

Climate Projections

Climate projections are scientifically modelled estimates of future temperature, rainfall, and extreme weather patterns based on different greenhouse gas emission scenarios. Estimates are typically made up to the end of the century

Cold Days

Percentage of days when the maximum temperature is less than the 10th percentile

Consecutive Dry Days (CDD)

Maximum number of consecutive dry days per time period with daily precipitation amount of less than 1 mm

DJF

December–January–February period

HWDI

Heat Wave Duration Index. The number of heat wave periods not less than 5 days

HWFI

Heat Wave Frequency Index. The maximum number of consecutive days per year when the daily maximum temperature is above the 90th percentile

JJAS

An acronym referring to the four-month period of June–July–August–September, which constitutes the core southwest monsoon season

MAM

March–April–May period

Maximum Temperature

The highest air temperature recorded in a day

Minimum Temperature

The lowest air temperature recorded in a day

OND

An acronym referring to the three-month period of October-November-December, which constitutes the core Northeast monsoon season

Southwest Monsoon

This occurs during the months of June to September. The southwest monsoon is India’s main rainy season and a lifeline for the country’s economy and ecology. It supports farming, fills rivers and lakes, and recharges groundwater. About 75 per cent of India’s total rainfall comes during this season, making it essential for irrigation, drinking water, and even electricity generation through hydropower.

Northeast Monsoon

This rainy season occurs from October to December and is also known as the retreating monsoon.

Rainy day

A rainy day, according to the India Meteorological Department, is defined as any day receiving >2.5 mm rainfall

Representative Concentration Pathways (RCPs)

Concentration pathways used by the Intergovernmental Panel on Climate Change (IPCC). They are prescribed pathways for greenhouse gas and aerosol concentrations, together with land use change, that are consistent with a set of broad climate outcomes used for climate modelling. The pathways are characterised by the radiative forcing produced by the end of the 21st century. Radiative forcing is the extra heat the lower atmosphere will retain as a result of additional greenhouse gases, measured in Watts per square metre (W/m²). There are four RCPs:

• RCP2.5: low pathway where radiative forcing peaks at approximately 3 W m-2 before 2100)

• RCP4.5 and RCP6.0 (two intermediate stabilisation pathways in which radiative forcing is stabilised at approximately 4.5 W m-2 and 6.0 W m-2 after 2100)

• RCP8.5 (high pathway for which radiative forcing reaches greater than 8.5 W m-2 by 2100)

RX1DAY

Highest 1-Day precipitation amount

RX5DAY

Highest consecutive 5-Day precipitation amount