The scientific activities related to the evolution of agrosystems and natural ecosystems with global changes strongly rely on an Environmental observatory.
The Kabini CZO / SNO M-TROPICS
Known as the Kabini Critical Zone Observatory in India and as the Indian sites of the SNO M-TROPICS in France, the observatory is supported by IISc, INSU, IRD and UPS. Its objective is to acquire, over the long term (several decades), the basic weather, hydrological and geochemical timeseries needed for assessing water and biogeochemical budgets in :
– a pristine forested ecosystem, the Mule Hole experimental watershed (4.1 km2, 11°720N and 76°420E) located in the core area of the Bandipur National Park, under sub-humid tropical climate, set up in 2003
– an agrossytem, the Berambadi experimental watershed (84km2, 11°47’5N and 76°39’3E) located aside Bandipur under sub-humid to semi-arid tropical climate and set up in 2010. The Berambadi watershed has also become, over the years, a Cal-val site for satellite observations, in particular for soil moisture.
The dataset collected by the observatory are in open access here.
Climate
Climate in south India is controlled by monsoon’s periodicity with alternate dry and wet seasons. The dry season extends from mid-December to May and the wet season starts with the southwest monsoon from May to September and ends with the northeast monsoon from October to December.
The Mule Hole catchment is part of the Bandipur National Park in the climatic transition zone. The mean annual rainfall is 1170 ± 260 mm/yr since 2003. The mean temperature is 22°C per year. The potential evapotranspiration is about 1050 mm/yr. The average aridity index, defined as the ratio between rainfall and potential evapotranspiration is 1.2. The climate can be classified as tropical sub-humid.
The Berambadi catchment is located at the western limit of the Bandipur Park, in slightly drier conditions than Mule Hole with mean annual rainfall of 900mm/yr upstream (western part) and 700mm/yr downstream (eastern part), i.e. close to semi-arid climate. The potential evapotranspiration is about 1100 mm/yr and the aridity index ranges from 0.6 to 0.75.
Geology
Parent rocks consist of peninsular gneiss intermingled with much less abundant enclaves of mafic to ultramafic rocks, mostly amphibolite. The dip angle of the gneissic units, composed in various proportions of quartz, Na-plagioclase (oligoclase), sericite and biotite, ranges from 75° to the vertical. The bedrock is covered by an immature saprolite, 15 m thick on average but with a large spatial variability, itself overlaid by a 0.5 to 2 m topsoil.
Soils
Topsoil mainly composed of 1-2 m thick Ferralsols on hillslopes and shallow ones (<0.5 m) on hilltop. Vertisols are often deep (>2 m) and present in valley bottoms and on amphibolite patches. They are composed of an assemblage secondary clays (kaolinite and goethite and smectites in vertisols) and residual quartz, sericite and plagioclase.
Hydrology and hydrogeology
The Mule Hole stream is highly ephemeral and flows only in response to heavy rainfall events, typically for a few hours to a few days. Over the period of observation, annual runoff ranged from 1 mm (2003) to 181 mm (2005).
The Berambadi stream is permanently dry since the 90’s because of the intensive groundwater pumping and numerous check dams along the stream network. The stream of Maddur (7.1 km2), an upstream sub-catchment, was continuously flowing the whole year, with a very low discharge rate during the dry season, until it became ephemeral in 2012 (a weak monsoon year). The aquifer of both watersheds is composed of the fractured bedrock, which has very low porosity (< 1 %) but good hydraulic conductivity, overlaid by the saprolite layer which has a high porosity (10-20 %) but a low hydraulic conductivity. Groundwater is mainly located in the fractured zone, because of the deep water uptake by vegetation at Mule Hole and of groundwater pumping in Berambadi.
Land cover and land use
The Mule Hole catchment is covered with a pristine, dry deciduous forest with, as species assemblage (70% of watershed area), Anogeissus latifolia, Terminalia alata and Tectona grandis Lagerstroemia microcarpa (so-called ATT facies), and understory Themeda triandra (Elephant grass) and the invasive species Lantana camara. Ceristoides trees are associated with Swamp vegetation. The Shorea vegetation type (Shorea roxburghii and Lagerstroemia microcarpa) covering about 15% of the catchment occurs on very shallow red soil overlying a sandy gneiss saprolite (0.2–0.4 m below the topographic surface).
The Berambadi catchment comprises on the upstream, western part, a dry deciduous forest which belongs to the Bandipur Park, and is constituted by the same type of vegetation than Mule Hole (although significantly degraded). The centre and Eastern parts (approximately 60 km2) are cultivated and inhabited (13 villages and hamlets). Three decades ago, land use was mostly rainfed agriculture, with crops such as finger millet, sorghum and pulses cultivated during the monsoon season. The introduction of tube wells in the 90s led to the development of intensive irrigated agriculture, first in the valleys and then across the catchment, with cash crops such as sugarcane, banana, turmeric and vegetables.
