Arrival Of Rainfall Research Articles

Regional Rainfall Regimes Affect the Sensitivity of the Huff Quartile Classification to the Method of Event Delineation

The widely used Huff quartile approach classifies rainfall events according to which quarter of their duration contains the largest rainfall depth. The rainfall events themselves are often delineated by specifying a minimum rainless interevent time (MIT) that must precede and follow a period of rainfall for it to be identified as a separate event. However, there is no standard or universally applicable value of this MIT criterion. Some studies have stipulated as little as 15 rainless minutes to mark the start of a new event, whilst others have required 24 h or more. The present work investigates how the adoption of different values of the MIT criterion, based, for instance, on the response time of a catchment or the drying time of a vegetation canopy, affects the Huff quartile classification. To date, this has not been explored. To address this issue, the Huff classification is herein applied to data from two Australian ground observing stations, one arid continental and one wet tropical. For each location, rainfall events were delineated using values of the MIT criterion ranging from 30 min to 24 h. In comparison with the 6 h MIT adopted by Huff (1967) as being appropriate for locations in the eastern USA, results show that, for instance, the proportion of events classified as 4Q ranges from 70.9% larger when events are delineated with a MIT = 30 min to 50.8% smaller when events are delineated using a MIT = 24 h. Moreover, the changes in the Huff classification that result from the use of different MIT values were not the same in wet tropical and arid locations. It is argued here that these findings reflect complexity in the arrival of rainfall, including differences in event duration and intraevent intermittency, that cannot be captured in the Huff classification system. Relevant rainfall regime characteristics such as these are likely to vary geographically, and the differences shown between the eastern USA and the two Australian locations are only examples of what is likely a more general effect. The results show that there is no single and generally applicable ‘Huff classification’ process, and that rather than a 6 h MIT being applicable everywhere, different MIT durations are needed in locations having differing rainfall regimes.

Preliminary result of capturing the signature of heavy rainfall events using the 2-d-/4-d water vapour information derived from GNSS measurement in Hong Kong

Apart from the well-known applications like positioning, navigation and timing (PNT), Global Navigation Satellite System (GNSS) has manifested its ability in many other areas that are vital to society largely. With the dense setting of the regional continuously operating reference station (CORS) networks, monitoring the variations in atmospheric water vapour using a GNSS technique has become a focus in the field of GNSS meteorology. Most previous studies mainly concentrate on the analysis of relationship between the two-dimensional (2-d) Precipitable Water Vapour (PWV) and rainfall while the three-dimensional (3-d) variations of atmospheric water vapour derived from the GNSS tomographic technique are more rarely discussed. In this work, we investigate changes in the emerging field of GNSS technology for monitoring changes in 2-d/3-d atmospheric water vapour during rainfall period. The signature of atmospheric water vapour variation was captured using the ground-based GNSS observations from the CORS network of Hong Kong which presents the particularity of being dense. In addition, the corresponding rain gauges and radiosonde stations are also used. Our analysis of the 2-d PWV/3-d water vapour profiles changes during the arrival, occurrence and depression of heavy rainfall shows that: (i) PWV increases before the arrival of heavy rainfall (ii) and decreases to its average value after the depression of rainfall; (iii) rainfall leads to an anomalous variation in relative humidity and temperature while their trends are totally opposite; (iv) atmospheric water vapour presents unstable conditions with intense vertical convective and horizontal convergence motions and hydrometeors are formed before the arrival of rainfall. This study indicates the potential of using GNSS technique to monitor spatio-temporal variations of atmospheric water vapour during rainfall period, which provides a better understanding of the mechanism of convection and rainfall induced by the extreme weather events.

Identification of Drought Prone Areas and Trend Analysis of Rainfall Phenomenon in Dhasan Basin

The present study has been focussed to recognize and quantify the drought condition in Dhasan basin which falls in drought prone region of Bundelkhand (Madhya Pradesh). The area is under frequent occurrence of droughts since decades due to irregularity in arrival of rainfall. The high variability of the annual rainfall is one of the primary causes of the drought prevailing in the Dhasan basin on a regular basis. The decreasing trend of rainfall may further aid to drought severity. The rainfall departure analysis indicated that, the study area is under the grip of regular and continuous droughts with the drought frequency varying between once in 2 years to once in 3 years, which is rather very high. Sagar and Banda areas were identified to be most drought prone followed by Khurai.

Heavy rainfall in the Kedarnath valley of Uttarakhand during the advancing monsoon phase in June 2013.

During the monsoon season of 2013, the advance of monsoon over northwest (NW) Indian region showed large abnormality as arrival of rainfall over Punjab, Himachal Pradesh (HP), Uttarakhand, Haryana and Delhi occurred between 13 and 16 June 2013, nearly twice the standard deviation earlier than normal. Such an early arrival by mid-June has been exceptional. The event was marked by unprecedented very heavy rainfall between 14 and 18 June 2013 over different meteorological sub-divisions of NW India. The event also led to human tragedy in Uttarakhand, in which many local people and pilgrims lost their lives. This heavy rainfall in fact moved from Punjab and HP during 14 and 15 June 2013 to Uttarakhand. The rainfall between 14 and 18 June 2013 over NW India was highly organized and it was continuously sustained with mesoscale enhanced intensity over Uttarakhand, which dispels the opinion about cloudburst. The present communication is aimed to study the observational aspects of the vigorous and rapid advance of monsoon rainfall over NW India and its intensification during 15-17 June 2013 over Uttarakhand.

Dynamic root distributions in ecohydrological modeling: A case study at Walnut Gulch Experimental Watershed

[1] Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. In particular, the rooting strategies employed by vegetation can be critical to their survival. However, land surface models currently prescribe rooting profiles as a function of only the plant functional type of interest with no consideration for the soil texture or rainfall regime of the region being modeled. Additionally, these models do not incorporate the ability of vegetation to dynamically alter their rooting strategies in response to transient changes in environmental forcings or competition from other plant species and therefore tend to underestimate the resilience of these ecosystems. To address the simplicity of the current representation of roots in land surface models, a new dynamic rooting scheme was incorporated into the framework of the distributed ecohydrological model tRIBS+VEGGIE. The new scheme optimizes the allocation of carbon to the root zone to reduce the perceived stress of the vegetation, so that root profiles evolve based upon local climate and soil conditions. The ability of the new scheme to capture the complex dynamics of natural systems was evaluated by comparisons to hourly timescale energy flux, soil moisture, and vegetation growth observations from the Walnut Gulch Experimental Watershed, Arizona. Robust agreement was found between the model and observations, providing confidence that the improved model is able to capture the multidirectional interactions between climate, soil, and vegetation at this site.

Identifying the optimal spatially and temporally invariant root distribution for a semiarid environment

In semiarid regions, the rooting strategies employed by vegetation can be critical to its survival. Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. Vegetation roots have strong control over this partitioning, and assuming a static root profile, predetermine the manner in which this partitioning is undertaken.A coupled, dynamic vegetation and hydrologic model, tRIBS + VEGGIE, was used to explore the role of vertical root distribution on hydrologic fluxes. Point‐scale simulations were carried out using two spatially and temporally invariant rooting schemes: uniform: a one‐parameter model and logistic: a two‐parameter model. The simulations were forced with a stochastic climate generator calibrated to weather stations and rain gauges in the semiarid Walnut Gulch Experimental Watershed (WGEW) in Arizona. A series of simulations were undertaken exploring the parameter space of both rooting schemes and the optimal root distribution for the simulation, which was defined as the root distribution with the maximum mean transpiration over a 100‐yr period, and this was identified. This optimal root profile was determined for five generic soil textures and two plant‐functional types (PFTs) to illustrate the role of soil texture on the partitioning of moisture at the land surface. The simulation results illustrate the strong control soil texture has on the partitioning of rainfall and consequently the depth of the optimal rooting profile. High‐conductivity soils resulted in the deepest optimal rooting profile with land surface moisture fluxes dominated by transpiration. As we move toward the lower conductivity end of the soil spectrum, a shallowing of the optimal rooting profile is observed and evaporation gradually becomes the dominate flux from the land surface. This study offers a methodology through which local plant, soil, and climate can be accounted for in the parameterization of rooting profiles in semiarid regions.