Meta-Analysis in Using Satellite Precipitation Products for Drought Monitoring: Lessons Learnt and Way Forward

In recent years, satellite precipitation products (SPPs) have emerged as an essential source of data and information. This work intends to summarize lessons learnt on using SPPs for drought monitoring and to propose ways forward in this field of research. A thorough literature review was conducted to review three aspects: effects of climate type, data record length, and time scale on SPPs performance. The conducted meta-analysis showed that the performance of SPPs for drought monitoring largely depends upon the climate type of the location and length of the data record. SPPs drought monitoring performance was shown to be higher in temperate and tropical climates than in dry and continental ones. SPPs were found to perform better with an increase in data record length. From a general standpoint, SPPs offer great potential for drought monitoring, but the performance of SPPs needs to be improved for operational purposes. The present study discusses blending SPPs with in situ data and other lessons learned, as well as future directions of using SPPs for drought applications.

Design flood estimation with varying record lengths in Norway under stationarity and nonstationarity scenarios

In traditional flood frequency analysis, a minimum of 30 observations is required to guarantee the accuracy of design results with an allowable uncertainty; however, there has not been a recommendation for the requirement on the length of data in NFFA (nonstationary flood frequency analysis). Therefore, this study has been carried out with three aims: (i) to evaluate the predictive capabilities of nonstationary (NS) and stationary (ST) models with varying flood record lengths; (ii) to examine the impacts of flood record lengths on the NS and ST design floods and associated uncertainties; and (iii) to recommend the probable requirements of flood record length in NFFA. To achieve these objectives, 20 stations with record length longer than 100 years in Norway were selected and investigated by using both GEV (generalized extreme value)-ST and GEV-NS models with linearly varying location parameter (denoted by GEV-NS0). The results indicate that the fitting quality and predictive capabilities of GEV-NS0 outperform those of GEV-ST models when record length is approximately larger than 60 years for most stations, and the stability of the GEV-ST and GEV-NS0 is improved as record lengths increase. Therefore, a minimum of 60 years of flood observations is recommended for NFFA for the selected basins in Norway.

Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management

Hydroclimatic extremes such as intense rainfall, floods, droughts, heatwaves, and wind or storms have devastating effects each year. One of the key challenges for society is understanding how these extremes are evolving and likely to unfold beyond their historical distributions under the influence of multiple drivers such as changes in climate, land cover, and other human factors. Methods for analysing hydroclimatic extremes have advanced considerably in recent decades. Here we provide a review of the drivers, metrics, and methods for the detection, attribution, management, and projection of nonstationary hydroclimatic extremes. We discuss issues and uncertainty associated with these approaches (e.g. arising from insufficient record length, spurious nonstationarities, or incomplete representation of nonstationary sources in modelling frameworks), examine empirical and simulation-based frameworks for analysis of nonstationary extremes, and identify gaps for future research.

Record Length Chrome Liner Run Using Innovative, Low-Marking, Non-Ferrous Dies on a Mechanical Casing Running Tool

Abu Dhabi National Oil Company (ADNOC) has steadily advanced toward the use of a casing running tool (CRT) vs. conventional casing running methods to improve efficiency and safety. This advancement focused mainly on 9 ⅝ in to 20 in diameter casing and utilized internal grip tools. Recently they have searched for an external-grip CRT system that would allow them to effectively run the smaller diameter liners of both ferrous and chrome (Cr) materials, especially in the extended reach drilling (ERD) wells with maximum reservoir contact (MRC). For 20 years CRT companies manufactured tools with gripping dies that could efficiently run ferrous material liners. Development of gripping mechanisms which can effectively run corrosion resistant alloy (CRA) materials has been met with varying success. Some of the challenges are to manufacture gripping dies from non-ferrous materials that will not contaminate the CRA liner and develop a gripping pattern that does not mark the CRA liner more than is accepted by API 5CRA industry standards, but maintain effective gripping force. In addition to hoisting and making up the string with no slippage it needs to perform fluid circulation at 3,000 psi. Until recently the liners were typically run in a conventional method using power-tongs. One of the tools chosen for the trial runs was a well-proven, external-grip mechanical CRT designed specifically for smaller diameter casing and liners. It has a 500-ton hoist capacity and a 5,000 psi circulation rating and was packaged with a combination float and cushion tool and a wireless torque turn sub. Dies had been designed to meet the non-contamination and acceptable marking criteria previously mentioned and would be compatible with liners possessing as much as 25% Cr. The dies had been extensively lab-tested, including heavy pull tests and torque application tests, but had not previously been used in field applications. The ERD-MRC well chosen for this trial was planned to have a record length of 6 ⅝ in, 24 ppf, 13% Cr liner with a wedge thread premium connection. In addition to not contaminating the liner, ADNOC expected an average running speed in joints per hour equivalent to the conventional casing running methods and a reduction in time during circulations. The result of the trial was 589 connections (25,035 ft liner length) successfully run with an average running speed matching their expectations. The liner displayed very minimal marks and there were no issues when hoisting or torqueing the connections. In addition, there were no rejected connections during the run. This publication will review the preparation for the run, actual run details, photos of the die marks, torque graphs and conclusions expressed by the operator with recommendations for changes moving forward.

A method for simulating risk profiles of wheat yield in data-sparse conditions

Process-based crop models are a robust approach to assess climate impacts on crop productivity and long-term viability of cropping systems. However, these models require high-quality climate data that cannot always be met. To overcome this issue, the current research tested a simple method for scaling daily data and extrapolating long-term risk profiles of modelled crop yields. An extreme situation was tested, in which high-quality weather data was only available at one single location (reference site: Snowtown, South Australia, 33.78°S, 138.21°E), and limited weather data was available for 49 study sites within the Australian grain belt (spanning from 26.67 to 38.02°S of latitude, and 115.44 to 151.85°E of longitude). Daily weather data were perturbed with a delta factor calculated as the difference between averaged climate data from the reference site and the study sites. Risk profiles were built using a step-wise combination of adjustments from the most simple (adjusted series of precipitation only) to the most detailed (adjusted series of precipitation, temperatures and solar radiation), and a variable record length (from 10 to 100 years). The simplest adjustment and shortest record length produced bias of modelled yield grain risk profiles between −10 and 10% in 41% of the sites, which increased to 86% of the study sites with the most detailed adjustment and longest record (100 years). Results indicate that the quality of the extrapolation of risk profiles was more sensitive to the number of adjustments applied rather than the record length per se.

Uncertainty in SPI Calculation and its Impact on Drought Assessment in Different Climate Regions over China

Uncertainty in the calculation of a Standardized Precipitation Index (SPI) attracted growing concerns in the hydrometeorology research community in the last decade. This issue is addressed in the present study from the perspective of candidate probability distributions, the data record length, the cumulative timescale and the selection of a reference period with the bootstrap and Monte Carlo methods using daily precipitation data observed in four climate regions across China. The impacts of the uncertainty in an SPI calculation on drought assessment are also investigated. Results show that the Gamma distribution is optimal in describing the cumulative precipitation in China; among the four timescales investigated in the present study, the minimal timescale appropriate for SPI calculation is 20 days for the humid region, 30 days for the semi-humid/semi-arid region and Tibetan Plateau (mostly its eastern part), and 90 days for the arid region. The uncertainty in SPI calculation decreases with the increase of timescale and record length, essentially as a consequence of the decrease of the confidence interval width of Gamma distribution parameters with the increase of timescale and record length. But there is little improvement for the parameter estimation with record length longer than 70 years. There is greater uncertainty for high absolute SPI values than for small ones, consequently there is greater uncertainty in assessing extreme droughts than moderate droughts. Reference period selection has large impacts on drought assessment, especially in the context of climate change. The uncertainty of the SPI calculation has large impacts on categorizing droughts, but no impact on assessing the temporal features of drought variation.

Sub-Basalt Imaging Reveals Deeper Plays Offshore India

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30279, “Revealing Deeper Plays, Offshore Kutch, India: A Success Story of Sub-Basalt Imaging,” by S.K. Biswal, N.N.B. Naidu, and S. Basu, ONGC, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2-6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. The Deccan Traps volcanic province of India is considered one of the largest basalt-covered regions in the world but is essentially unexplored because of the limitations of conventional marine streamer P-wave seismic acquisition in imaging structures both intrabasalt and sub-basalt. In the complete paper, the authors demonstrate that, even with legacy marine streamer surveys, an appropriate work flow of combining suitable advanced technologies can help to overcome the long-standing challenges of sub-basalt imaging. The reprocessed data show clear uplift in sub-basalt imaging, and inversion results validate the quality of the new data in relation to the well logs. Introduction The Kutch offshore basin is characterized by the presence of the Deccan Traps, a large igneous province of up to 2000-m-thick basalt lava flows. These lava flows have hindered successful imaging of sub-basalt Mesozoic sediments for hydrocarbon exploration. To date, no single technique has been found to produce considerable improvements in deeper image quality. The solution lies in an appropriate combination of advanced technologies. The project consists of three legacy data sets acquired in 2004, 2010, and 2014 in the shallow-water area (water depth ranges from 25 to 50 m). Two of the surveys were shot in the north/south direction with six streamers having 100-m separation, 25-m shot spacing, 12.5-m receiver spacing, and 6-second record length. The third survey was acquired oblique to these with a similar acquisition geometry; however, it featured sparser 25-m receiver spacing and 8- second record length. These surveys were matched and merged before migration to ensure a seamless image across the surveys in the post-migration domain. A tailored processing work flow improved existing data quality significantly and provided new insights into the sub-basalt geology, thereby opening a new play to exploration and production. Challenges and Work Flow Sub-basalt imaging challenges include transmission losses, scattering, complex wave kinematics, prevalent multiples, interference effects, and variable illumination caused by high and variable acoustic impedance of thick heterogeneous basalt layers. The tertiary sedimentary sequences overlying the Deccan Trap consist predominantly of carbonates, shale, and fine-grained clastic sediments, accompanied by channels and nearly vertical faulting. The geological complexities from the water bottom to the base of the basalt present a substantial geophysical challenge to successful deeper imaging and require an appropriate work flow to mitigate them. Broadband processing, including de-ghosting, can increase the signal-to-noise ratio across the broad range of frequencies in the seismic bandwidth and can enhance the lower frequencies required to achieve enhanced imaging at sub-basalt targets. Demultiple methods can reduce the presence of surface-related and interbed multiples that prohibit reliable interpretation of Mesozoic sediment; imaging methods can focus the recorded data when used in conjunction with an accurate Earth model that captures the velocity complexities of carbonates, shale, basalt, channel, and faults.

Uncertainty Analysis of Hydrological Drought due to Record Length, Time Scale, and Probability Distribution Functions Using Monte-Carlo Simulation Method

Standardized Runoff Index (SRI), as one of the well-known hydrological drought indices, may contain uncertainties caused by the employment of the distribution function, time scale, and record length of statistical data. In this study, the uncertainty in the SRI estimation of monthly discharge data of 30 and 49 year length from Minab dam watershed, south of Iran, was investigated. Four probability distribution functions (Gamma, Weibull, Lognormal, and Normal) were used to fit the cumulative discharge data at 3, 6. 9, 12, 24 and 48 month time scales, with their goodness-of-fit and normality evaluated by K-S and normality tests, respectively. Using Monte-Carlo sampling, 50,000 statistical data were generated for each event and each time scale, followed by 95% confidence interval. The width of the confidence interval was used as uncertainty and sources of uncertainty were investigated using miscellaneous factors. It was found that the maximum uncertainty was related to normal and lognormal distributions and the minimum uncertainty to gamma and Weibull distributions. Further, the increase in both time scale and record length led to the decrease in uncertainty.

Effects of acquisition device, sampling rate, and record length on kinocardiography during position-induced haemodynamic changes

Background Kinocardiography (KCG) is a promising new technique used to monitor cardiac mechanical function remotely. KCG is based on ballistocardiography (BCG) and seismocardiography (SCG), and measures 12 degrees-of-freedom (DOF) of body motion produced by myocardial contraction and blood flow through the cardiac chambers and major vessels. Results The integral of kinetic energy ($$ iK$$ iK ) obtained from the linear and rotational SCG/BCG signals was computed over each dimension over the cardiac cycle, and used as a marker of cardiac mechanical function. We tested the hypotheses that KCG metrics can be acquired using different sensors, and at 50 Hz. We also tested the effect of record length on the ensemble average on which the metrics were computed. Twelve healthy males were tested in the supine, head-down tilt, and head-up tilt positions to expand the haemodynamic states on which the validation was performed. Conclusions KCG metrics computed on 50 Hz and 1 kHz SCG/BCG signals were very similar. Most of the metrics were highly similar when computed on different sensors, and with less than 5% of error when computed on record length longer than 60 s. These results suggest that KCG may be a robust and non-invasive method to monitor cardiac inotropic activity. Trial registration Clinicaltrials.gov, NCT03107351. Registered 11 April 2017, https://clinicaltrials.gov/ct2/show/NCT03107351?term=NCT03107351&draw=2&rank=1.

Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management

Hydroclimatic extremes such as intense rainfall, floods, droughts, heatwaves, and wind/storms have devastating effects each year. One of the key challenges for society is understanding how these extremes are evolving and likely to unfold beyond their historical distributions under the influence of multiple drivers such as changes in climate, land cover, and other human factors. Methods for analysing hydroclimatic extremes have advanced considerably in recent decades. Here we provide a review of the drivers, metrics and methods for the detection, attribution, prediction and projection of nonstationary hydroclimatic extremes. We discuss issues and uncertainty associated with these approaches (e.g arising from insufficient record length, spurious nonstationarities, or incomplete representation of nonstationary sources in modelling frameworks), examine empirical and simulation-based frameworks for analysis of nonstationary extremes, and identify gaps for future research.