China-Z Index Research Articles

Comparison of drought indices for appraisal of drought characteristics in the Ken River Basin

Drought indices are used to monitor drought conditions of a region. Various drought indices (DIs) have been proposed in past few decades, but some of those are region specific and have limitations of applicability in other climatic conditions. Also, multiple time steps of DIs make it hard to decide that which time step is the best to show the drought condition.Present study aims to compare Standardized Precipitation Index (SPI), Effective Drought Index (EDI), statistical Z-Score, China Z-Index (CZI), Rainfall Departure (RD), Rainfall Decile based Drought Index (RDDI) for their suitability in drought prone districts of the Ken River Basin, located in central India, where the rainfall is concentrated in the monsoon season (June–September) and frequent occurrence of severe drought events are common. All selected DIs with multiple time steps are applied to compute the severity for five time steps of 1, 3, 6, 9, and 12-month, and compared with each other and EDI.The study reveals that (1) 1-month time step in all DIs may produce erroneous estimates of drought duration. (2) The drought indices computed for 9-month time step are best correlated with each other. However, the drought duration and the drought frequencies estimated using RD and RDDI are in disagreement with other DIs, therefore, these are not suitable for this area where the summer concentration of precipitation is very high. (3) The DIs are highly correlated at same time steps and can alternatively be used. However, they are poorly correlated at dissimilar time steps, which makes it hard to assess whether the drought occurred or not. (4) Because there are no objective rules to select the appropriate time step, and the identified drought duration varies too much with different time steps, it is very hard again to assess when the drought occurred.However, EDI, that has self-defined time step in itself, and free from time step problem, (1) is correlated better with other DIs for all time steps and effective on long and short drought together, with highest correlation at 9-month time steps, (2) identifies the drought condition earlier than any other indices, therefore, (3) is found to be more suitable drought index for the study basin. This is in agreement with the result of EDI application in Korea, Japan, Turkey, Australia and Iran though the methods of its testing are different.

Study on the Quantification of Drought in Freshwater Wetlands——A Case Study in Baiyangdian Wetland

Drought index is an important tool for monitoring and evaluation. A new drought index for freshwater wetlands is developed based on water balance, then used to evaluate drought in Baiyangdian Wetland (BW). Choosing the high resolution data——daily water stage (if not available, choose monthly data alternatively) as input data to compute the Wetland Drought Index (WDI). The results may be presented in monthly, seasonal or annual scale, such as Standard Precipitation Index (SPI). Daily data was used in calculating WDI during 1960 to 1986, and the results are revealed in monthly, seasonal and annual time scale to compare with SPI and China Z Index (CZI). The results of WDI are in accordance with the local record of wetland drought (Anxin county annals, 2000), while the other indices are not. Daily data produce the most precise dating of droughts, but these data were not available after 1986, therefore monthly data were used. For the period before 1986, comparisons using monthly data and daily data identify the same droughts, and show only minor differences in resolving drought onset and termination dates. During 1960 to 2008, the frequency of drought was increasing, mainly because of the low precipitation and controlling of reservoirs upstream. There are five mainly drought periods identified by WDI during this time: 1965 ~ 1967, 1972 ~ 1973, 1975 ~ 1976, 1980 ~ 1986 and 2000 ~ 2008, which are not identified by SPI and CZI.

Meteorological drought monitoring using several drought indices (case study: Salt Lake Basin in Iran)

Drought detecting is a necessary aspect of drought risk management. It is generally performed usingdifferent drought indices that are effectively continuous functions of rainfall and other hydro- meteorologicalvariables. A number of drought indices have been introduced and used in various countries to date. In thecurrent research, four meteorological drought indices including the standardized precipitation index (SPI),China-Z index (CZI), modified CZI (MCZI) and Z-Score (Z) are compared and evaluated for monitoringdroughts in Salt Lake Basin in Iran. The comparison of indices was carried out based on drought classes thatwere monitored in the study area using 40 years of data. The results indicated that SPI, CZI and Z-Scoreperformed similarly with regard to drought identification and responded slowly to drought onset. DI appearedto be very sensitive to precipitation rates, but had unsteady spatial and temporal variation. Additionally, byconsidering the advantages and disadvantages of the mentioned drought predictors in Iran, the CZI and ZScorecould be used as good meteorological drought predictors.

Spatio-Temporal Analysis of Droughts in Semi-Arid Regions by Using Meteorological Drought Indices

Six meteorological drought indices including percent of normal (PN), standardized precipitation index (SPI), China-Z index (CZI), modified CZI (MCZI), Z-Score (Z), the aridity index of E. de Martonne (I) are compared and evaluated for assessing spatio-temporal dynamics of droughts in six climatic regions in Iran. Results indicated that by consideration of the advantages and disadvantages of the mentioned drought predictors in Iran, the Z-Score, CZI and MCZI could be used as a good meteorological drought predictor. Depending on the month, the length of drought and climatic conditions of the region, they are an alternative to the SPI that has limitations both because of only a few available long term data series in Iran and its complex structure.

Comparison of multi-monthly rainfall-based drought severity indices, with application to semi-arid Konya closed basin, Turkey

Summary Many drought indices (DIs) have been introduced to monitor drought conditions. This study compares Percent of Normal (PN), Rainfall Decile based Drought Index (RDDI), statistical Z-Score, China-Z Index (CZI), Standardized Precipitation Index (SPI), and Effective Drought Index (EDI) to identify droughts in a semi-arid closed basin (Konya), Turkey. Comparison studies of DIs under different climatic conditions is always interesting and may be insightful. Employing and comparing 18 different timesteps, the objective of comparison is twofold: (1) to determine the effect of timestep for choosing an appropriate value, and (2) to determine the sensitivity of DI to timestep and the choice of a DI. Monthly rainfall data obtained from twelve spatially distributed stations was used to compare DIs for timesteps ranging from 1 month to 48 months. These DIs were evaluated through correlations for various timesteps. Surprisingly, in many earlier studies, only 1-month time step has been used. Results showed that the employment of median timesteps was essential for future studies, since 1-month timestep DIs were found as irrelevant to those for other timesteps in arid/semi-arid regions because seasonal rainfall deficiencies are common there. Comparing time series of various DI values (numerical values of drought severity) instead of drought classes was advantageous for drought monitoring. EDI was found to be best correlated with other DIs when considering all timesteps. Therefore, drought classes discerned by DIs were compared with EDI. PN and RDDI provided different results than did others. PN detected a decrease in drought percentage for increasing timestep, while RDDI overestimated droughts for all timesteps. SPI and CZI were more consistent in detecting droughts for different timesteps. The response of DI and timestep combination to the change of monthly and multi-monthly rainfall for a qualitative comparison of severities (drought classes) was investigated. Analyzing the 1973–1974 dry spell at Beysehir station, EDI was found sensitive to monthly rainfall changes with respect to cumulative rainfall changes, especially more sensitive than other DIs for shorter timesteps. Overall, EDI was consistent with DIs for various timesteps and was preferable for monitoring long-term droughts in arid/semi-arid regions. The use of various DIs for timesteps of 6, 9, and 12 months is essential for long term drought studies. 1-month DIs should not be used solely in comparison studies to present a DI, unless there is a specific reason. This investigation showed that the use of an appropriate timestep is as important as the type of DI used to identify drought severities.

Drought monitoring in Iran using the perpendicular drought indices

This paper aims at finding, evaluating and refining an appropriate drought estimation method for semi-arid regions, e.g., Iran using remote sensing. Recently developed methods, the Perpendicular Drought Index (PDI) and Modified Perpendicular Drought Index (MPDI), are selected as satellite based drought indices in this study. Time series of the Moderate Resolution Imaging Spectroradiometer (MODIS) images are collected over the region spanning the time interval from February 2000 to December 2005, and the PDI and MPDI are calculated. Then, these indices are evaluated against meteorological drought indices including Z-score (Z), China-Z Index (CZI) and Modified China-Z Index (MCZI) over 180 meteorological observing stations in Iran. The results show that there is a statistically significant correlation between the PDI and MPDI and regional surface dryness and drought conditions. It is further confirmed that the PDI is performing well for bare soil applications or early stages of vegetation growth, while the MPDI is best for vegetated surfaces yet effective for bare soils. Since Iran is characterized by semi-arid or arid climatic conditions, the perpendicular drought indices could be used as simple remote sensing-based drought indices in Iran and in other developing countries with similar climatic conditions.

Comparison of seven meteorological indices for drought monitoring in Iran

AbstractDrought monitoring is an essential component of drought risk management. It is normally performed using various drought indices that are effectively continuous functions of rainfall and other hydrometeorological variables. A number of drought indices have been introduced and applied in different countries to date. This paper compares the performance of seven indices for drought monitoring in the Tehran province of Iran. The indices used include deciles index (DI), percent of normal (PN), standard precipitation index (SPI), China‐Z index (CZI), modified CZI (MCZI), Z‐Score and effective drought index (EDI). The comparison of indices is based on drought cases and classes that were detected in the province over the 32 years of data, as well as over the latest 1998–2001 drought spell. The results show that SPI, CZI and Z‐Score perform similarly with regard to drought identification and respond slowly to drought onset. DI appears to be very responsive to rainfall events of a particular year, but it has inconsistent spatial and temporal variation. The SPI and EDI were found to be able to detect the onset of drought, its spatial and temporal variation consistently, and it may be recommended for operational drought monitoring in the Province. However, the EDI was found to be more responsive to the emerging drought and performed better. Copyright © 2006 Royal Meteorological Society

An evaluation of the Standardized Precipitation Index, the China‐Z Index and the statistical Z‐Score

AbstractThe Standardized Precipitation Index (SPI) was developed to detect drought and wet periods at different time scales, an important characteristic that is not accomplished with typical drought indices. More and more users employ the SPI to monitor droughts. Although calculation of the SPI is easier than other drought indices, such as the Palmer Drought Index, it is still relatively complex. In China, an index called the China‐Z Index (CZI) has been used since 1995 by the National Climate Centre of China to monitor moisture conditions across the country. The calculation of this index is easier than the SPI. A third index, the statistical Z‐Score, can also be used to monitor droughts. This paper evaluates the SPI, CZI and Z‐Score on 1‐, 3‐, 6‐, 9‐ and 12‐month time scales using monthly precipitation totals for four locations in China from January 1951 to December 1998 representing humid and arid climates, and cases of drought and flood. Advantages and disadvantages for the application of each index are compared. Study results indicate that the CZI and Z‐Score can provide results similar to the SPI for all time scales, and that the calculations of the CZI and Z‐Score are relatively easy compared with the SPI, possibly offering better tools to monitor moisture conditions. Copyright © 2001 Royal Meteorological Society