Monthly climatic water balance at selected locations in India

Meteorological data (1971-2000) for twenty seven (27) well distributed locations in India, have been utilized to compute average monthly rainfall (RF) and potential evapotranspiration (PET). In the present study, potential evapotranspiration (PET) has been calculated by using FAO recommended Penman-Monteith equation. An attempt has been made to identify the months of water deficit / surplus and these have been discussed in relation to crop planning for both seasons Monsoon or Kharif (June to September) and Rabi (October to February).In northwest, west and central zone, water deficit is observed at several stations in Kharif and all stations in Rabi. The average RF/PET ratio in this zone is 0.53 indicating that except in Pantnagar and Adhartal (0.94), crop selection and planning do not favour crops requiring more water. During Kharif season RF/PET ratio of several stations, except Hissar and Jodhpur, is more than 1, suggesting successful cropping with rainfall. In east and northeast zone, water surplus is observed at all the stations in Kharif. Water deficit in Rabi occurred at most of the places during December, January and February. RF/PET ratio during Kharif season ranges between 1.44 and 5.93 suggesting none of the stations undergo water deficit during the crop growing period. For the stations selected in south zone, water deficit in Kharif occurred at many places in the months of June, July and August. Water deficit in Rabi occurred at many places during January and February. During Kharif RF/PET ratio is less than 1 except for Rajamundry and Pattambi. This emphasizes the need for proper crop selection for successful cropping with limited moisture.

Global distribution of the rooting zone water storage capacity reflects plant adaptation to the environment

The rooting zone water storage capacity (S0) extends from the soil surface to the weathered bedrock (the Critical Zone) and determines land-atmosphere exchange during dry periods. Despite its importance to land-surface modeling, variations of S0 across space are largely unknown as they cannot be observed directly. We developed a method to diagnose global variations of S0 from the relationship between vegetation activity (measured by sun-induced fluorescence and by the evaporative fraction) and the cumulative water deficit (CWD). We then show that spatial variations in S0 can be predicted from the assumption that plants are adapted to sustain CWD extremes occurring with a return period that is related to the life form of dominant plants and the large-scale topographical setting. Predicted biome-level S0 distributions, translated to an apparent rooting depth (zr) by accounting for soil texture, are consistent with observations from a comprehensive zr dataset. Large spatial variations in S0 across the globe reflect adaptation of zr to the hydroclimate and topography and implies large heterogeneity in the sensitivity of vegetation activity to drought. The magnitude of S0 inferred for most of the Earth’s vegetated regions and particularly for those with a large seasonality in their hydroclimate indicates an important role for plant access to water stored at depth - beyond the soil layers commonly considered in land-surface models.

Magnolia and Viburnum Plant Factors at Different Growing Seasons and Allowed Depletion Levels in a Monsoonal Climate

We investigated seasonal water use, growth and acceptable root-zone water depletion levels to develop tools for the more precise irrigation of two Southeast U.S. landscape species in a monsoonal climate—Magnolia grandiflora and Viburnum odoratissimum. The study was conducted under a rainout shelter consisting of two concurrent studies. One, weighing lysimeter readings of quantified water use (ETA) at different levels of irrigation frequency that dried the root zone to different allowable depletion levels (ADL). Two, planting the same species and sizes inground and irrigating them to the same ADLs to assess the effect of root-zone water depletion on growth. The projected crown area (PCA) and crown volume were concurrently measured every three weeks in both studies as well as reference evapotranspiration (ETo). Plant factor values were calculated from the ratio of ETA (normalized to depth units by PCA) to ETo. The two species had different tolerances for irrigation frequency depending on the season: peak magnolia canopy growth was mid-spring to mid-summer, while peak viburnum canopy growth was summer. Canopy growth for both species was most sensitive to greater ADL-water stress during the peak growth stages of both species. For urban landscape irrigation, these data suggest that 60–75% of available water in magnolia and viburnum root zones can be depleted before irrigation and that they can be irrigated at a plant factor (PF) value of 0.6 of ETo. For landscape situations with high expectations, such as during establishment and especially during peak growth, a wetter water budget that minimizes water stress would be more appropriate: 30–45% ADL and PF values of 0.7–0.8. The results of this study are aimed at water managers and landscape architects and designers in a humid climate who need to account for water demand in planning scenarios.

Technical note: Accounting for snow in the estimation of root zone water storage capacity from precipitation and evapotranspiration fluxes

A common parameter in hydrological modeling frameworks is root zone water storage capacity (SR[L]), which mediates plant water availability during dry periods as well as the partitioning of rainfall between runoff and evapotranspiration. Recently, a simple flux-tracking-based approach was introduced to estimate the value of SR (Wang-Erlandsson et al., 2016). Here, we build upon this original method, which we argue may overestimate SR in snow-dominated catchments due to snow melt and evaporation processes. We propose a simple extension to the method presented by Wang-Erlandsson et al. (2016) and show that the approach provides a lower estimate of SR in snow-dominated watersheds. This SR dataset is available at a 1 km resolution for the continental USA, along with the full analysis code, on the Google Colab and Earth Engine platforms. We highlight differences between the original and new methods across the rain–snow transition in the Southern Sierra Nevada, California, USA. As climate warms and precipitation increasingly arrives as rain instead of snow, the subsurface may be an increasingly important reservoir for storing plant-available water between wet and dry seasons; therefore, improved estimates of SR will better clarify the future role of the subsurface as a storage reservoir that can sustain forests during seasonal dry periods and episodic drought.

Study of Composition and Composition of Macro Algae Habitat in the Intertidal Zone Water of Sibu Island, Nort Oba District Tidore Islands City Nort Maluku

Macro algae is a part of marine plants whose whole body is called the "thallus". Macro algae are widespread in tropical and sub-tropical waters. The purpose of this study was to determine the composition of the macro algae species, the width of the micro-habitat niches, and the overlapping of the micro-habitat niches in the intertidal zone of the waters of Sibu Island, Oba Utara District, Tidore Islands City. The data was collected using survey method using belt transects and squares measuring 1x1 m2 which are placed systematically in zigzags along the tansek belt. In this study, 20 species of macro algae were found in the waters of the island of Sibu, consisting of Halimeda macroloba, Halimeada opuntia forma chordata, Halimeda incrassata, Halimeda opuntia forma renschii, Chaetamorpha sp, Eucheuma cottonii, Sargassum duplicatum, S.polycestum, Turbina ornata, T. conoides, Padina boergesenii, Dictyota dichotoma, Amphiroa fragilissima, Acanthopora spicifera, Eucheuma denticulatum, E. spinosum, Glacilaria salicornia, Hypnea nidulans, Galaxaura apiculata. The results of the analysis of the width of the recesses showed that the macro algae species with the largest recess width were Eucheuma denticulatum with a value of 0.905, while Galaxura apiculata had the narrowest recess widths with a value of 0.200. Furthermore, based on the results of overlapping analysis of microhabitat niches, it shows that the overlap of microbaitate niches is quite large by Sargassum polycestum against Galaxaura apiculata with a value of 0.337, while the lowest was carried out by Halimeda macroloba against Galaxaura apiculata, Halimeda opuntia forma chordata against Galaxaura apiculata with a value of 0.337, while the lowest was carried out by Halimeda macroloba against Galaxaura apiculata, Halimeda opuntia forma chordata against Galaxaura apiculata, Eucheuma spinosum against Galaxaura apiculata with a value of 0.000.

Global carbon and water exchange during drought reflects adaptation of rooting depth to climate and topography

<p>The rooting zone water storage capacity (S) defines the total amount of water available to plants for transpiration during rain-free periods. Thereby, S determines the sensitivity of carbon and water exchanges between the land surface and the atmosphere, controls the sensitivity of ecosystem functioning to progressive drought conditions, and mediates feedbacks between soil moisture and near-surface air temperatures. While being a central quantity for water-carbon-climate coupling, S is inherently difficult to observe. Notwithstanding scarcity of observations, terrestrial biosphere and Earth system models rely on the specification of S either directly or indirectly through assuming plant rooting depth.</p><p>Here, we model S based on the assumption that plants size their rooting depth to maintain function under the expected maximum cumulative water deficit (CWD), occurring with a return period of 40 years (CWD<sub>X40</sub>), following Gao et al. (2014). CWD<sub>X40</sub> is “translated” into a rooting depth by accounting for the soil texture. CWD is defined as the cumulative evapotranspiration (ET) minus precipitation, where ET is estimated based on thermal infrared remote sensing (ALEXI-ET), and precipitation is from WATCH-WFDEI, modified by accounting for snow accumulation and melt. In contrast to other satellite remote sensing-based ET products, ALEXI-ET makes no a priori assumption about S and, as our evaluation shows, exhibits no systematic bias with increasing CWD. It thus provides a robust observation of surface water loss and enables estimation of S with global coverage at 0.05° (~5 km) resolution.</p><p>Modelled S and its variations across biomes is largely consistent with observed rooting depth, provided as ecosystem-level maximum estimates by Schenk et al. (2002), and a recently compiled comprehensive plant-level dataset. In spite of the general agreement of modelled and observed rooting depth across large climatic gradients, comparisons between local observations and global model predictions are mired by a scale mismatch that is particularly relevant for plant rooting depth, for which the small-scale topographical setting and hydrological conditions, in particular the water table depth, pose strong controls.</p><p>To resolve this limitation, we investigate the sensitivity of photosynthesis (estimated by sun-induced fluorescence, SIF), and of the evaporative fraction (EF, defined as ET over net radiation) to CWD. By employing first principles for the constraint of rooting zone water availability on ET and photosynthesis, it can be derived how their sensitivity to the increasing CWD relates to S. We make use of this relationship to provide an alternative and independent estimate of S (S<sub>dSIF</sub> and S<sub>dEF</sub>), informed by Earth observation data, to which S, modelled using CWD<sub>X40</sub>, can be compared. Our comparison reveals a strong correlation (R<sup>2</sup>=0.54) and tight consistency in magnitude between the two approaches for estimating S. </p><p>Our analysis suggests adaptation of plant structure to prevailing climatic conditions and drought regimes across the globe and at catchment scale and demonstrates its implications for land-atmosphere exchange. Our global high-resolution mapping of S reveals contrasts between plant growth forms (grasslands vs. forests) and a discrepant importance across the landscape of plants’ access to water stored at depth, and enables an observation-informed specification of S in global models.</p>

Stable isotope insights into dryland ecohydrology

<p>Isotopic tracing of water sources for plants is an increasingly common method that supports insight into climatic controls on water availability to plants and their use of this available water, especially in water-limited environments where isotopic endmembers are distinct. Recent advances in this field of research have enabled characterization of annual and seasonal water use by plants, whose water sources vary in contribution along a continuum between groundwater (isotopically light) to infiltrated precipitation (isotopically heavy). Xylem samples are commonly used to characterize real-time uptake of water from roots, and they can be contextualized with respect to endmember water sources via sampling of root zone water, providing these endmembers are isotopically distinct. The time integration of seasonally varying water source usage results in the annually recorded isotopic signal recorded in tree ring cellulose for temperate trees and shrubs, which reflects the dominant water source used in the season of growth. This has enabled dendro-isotopic methods that are commonly used to reconstruct past climates (isotopically light = colder/wetter; isotopically heavy = warmer/drier). However, questions have arisen about the utility of these annually integrated dendro-isotopic signatures, given the strong seasonal variations of water use that are particularly pronounced in dryland ecosystems, including notable water source switching by plants.      </p><p>In our recent work, we have been pushing isotopic methods in new directions to better understand what plants can tell us about how climate affected hydrology across dryland regions, and about the associated plant responses. Drylands pose interesting research challenges, since water is typically the key limiting factor on dryland plant growth, and it is fundamental to the health, functioning, composition, distribution, and evolution of vegetation communities. In drylands, water availability to plants may vary dramatically across space and time, creating challenges for simple analyses of annual water use signatures. To aid the understanding of climatically-controlled ecohydrology in drylands, we have developed a new tool (ISO-Tool) based on established biochemical fractionation theory, which allows for back-calculation of water sources used for growth from tree-ring isotopes. This tool generates critical knowledge for evaluating dendro-isotopic signatures within the same reference frame as sampled endmember water sources, and it can be used for both annual and seasonal analyses of plant water use. We have also been working on a set of interdisciplinary metrics we call water stress indicators (WSIs), which support corroboration of information on climatic forcing, water availability, plant water uptake, and ecological health of terrestrial vegetation.   </p><p>Using these new methods, we have been able to identify important hydroclimatic gradients in water usage for the same species that reflect the local expression of climate into plant-available water. We have also begun to understand the whole continuum from climate forcing to root-zone water availability to tree growth to canopy health. We believe this broader continuum perspective is critical for tackling key ecohydrological questions especially in drylands, where we expect large variability in water availability across space and time.         </p>

Developing a climate-driven root zone water stress function for different climates and ecosystems

<p>Plant roots have less water available when soils have low moisture content and, consequently, limit their root-to-leaf water potential gradient to protect their xylem, which reduces H<sub>2</sub>O and CO<sub>2</sub> exchanges with the atmosphere. In vegetation, hydrological and land-surface models, plant responses to reduced available water in the soil have been implemented in various ways depending on data availability, type of ecosystem, and modelling assumptions. Most models use soil water stress functions – commonly known as beta functions – to reduce transpiration and carbon assimilation, by applying a factor that reflects the soil water availability for plants. These functions usually produce reasonably satisfactory results, but rely on the information on soil properties (e.g. wilting point and field capacity) that are not widely available. On a global level, soil information is mediocre, and data uncertainty is compensated by tuning parameters that rarely represent a physiological process. We propose instead the use of a beta function derived from a mass-balance approach focused on the root zone water capacity. This method quantifies the root zone water storage by calculating the accumulated water deficit based on the balance between water influxes and effluxes, and it does not require land-cover or soil information. We assessed how our approach performs compared to those other soil water stress functions. We used global datasets, including WDFE5 and PMLv2, to extract precipitation and evapotranspiration and compute water deficit. For most vegetation types and climates our approach yielded promising results. Worst results were found for some (semi-)arid sites due to the overestimation of the water deficit. We aim to deliver an approach that can be easily applied on global scales.</p>